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# Schistosomiasis, a disease caused by a parasitic worm, is prevalent in

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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
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GMATNinja

How would you see the usage of that & which in this question.
in Statement A, B - that is used
in C, D, E - which is used.

can they be used interchangeably?
I quietly mentioned the issue of that vs. which in answer choices (C), (D), and (E), but I deliberately didn't say much about it.

Technically speaking, "that" is an essential modifier -- in other words, we wouldn't fully understand the meaning of the sentence without it -- and "which" is a non-essential modifier, meaning that it just provides some extra information. In general, modifiers beginning with "which" usually follow a comma. But unless they're part of a larger list, modifiers beginning with "that" usually do not follow a comma. Here, have a couple of examples:

• The GMAT book that is on the table is useless. --> The phrase "that is on the table" is an essential modifier, so the sentence implies that you wouldn't know exactly which GMAT book is useless if I didn't include the modifier. In other words, the sentence implies that there are some other books around -- maybe in the refrigerator, or on the bookshelf, or wherever -- and you need me to specify that the one on the table is the useless one.
• The GMAT book, which is on the table, is useless. --> Now "which is on the table" is just extra information. The sentence implies that there's only one GMAT book around, and it just happens to be on the table. But without the non-essential modifier, you'd still be able to identify the useless book.

The trouble is, either sentence is completely fine. They just mean slightly different things. In practice, it's really hard for the GMAT to test the distinction between essential and non-essential modifiers, and it's rarely -- if ever -- the deciding factor in official questions. Notice that you can absolutely get to correct answer on the schistosomiasis question without giving any thought to the difference between "which" and "that." And that's why I didn't say much about it in the explanation above.

But for what it's worth: yeah, "which" isn't a great choice in (C), (D), and (E), since "which" needs to be preceded by a comma, and it seems like the phrase "which become the parasite's hosts" is essential to the meaning of the sentence -- so it probably should start with "that" instead of "which." But in all three of those answer choices, there are arguably more significant issues.

I hope this helps!
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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
Kchaudhary
Schistosomiasis, a disease caused by a parasitic worm, is prevalent in hot, humid climates, and it has become more widespread as irrigation projects have enlarged the habitat of the freshwater snails that are the parasite's hosts for part of its life cycle.

(A) the freshwater snails that are the parasite's hosts for part of its life cycle - Correct

(B) the freshwater snails that are the parasite's hosts in part of their life cycle

(C) freshwater snails which becomes the parasite's hosts for part of its life cycles - SV Number agreement error and also ',' is missing before which

(D) freshwater snails which become the hosts of the parasite during the parasite's life cycles - ',' is missing before which

(E) parasite's hosts, freshwater snails which become their hosts during their life cycles - above errors + change in meaning

As we know that all pronoun refers to the one antecedent not different one, 'it' is non underlined part refers to Schistosomiasis where as 'its' in underlined part refers to parasite. therefore A can not be right answer,???

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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
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robu1
Kchaudhary
Schistosomiasis, a disease caused by a parasitic worm, is prevalent in hot, humid climates, and it has become more widespread as irrigation projects have enlarged the habitat of the freshwater snails that are the parasite's hosts for part of its life cycle.

(A) the freshwater snails that are the parasite's hosts for part of its life cycle - Correct

(B) the freshwater snails that are the parasite's hosts in part of their life cycle

(C) freshwater snails which becomes the parasite's hosts for part of its life cycles - SV Number agreement error and also ',' is missing before which

(D) freshwater snails which become the hosts of the parasite during the parasite's life cycles - ',' is missing before which

(E) parasite's hosts, freshwater snails which become their hosts during their life cycles - above errors + change in meaning

As we know that all pronoun refers to the one antecedent not different one, 'it' is non underlined part refers to Schistosomiasis where as 'its' in underlined part refers to parasite. therefore A can not be right answer,???

robu , from what source did you get the rule that there can be only one pronoun that must always refer only to the main subject of the main clause?

A pronoun needs to refer to the most logical antecedent -- to the antecedent that makes sense. In this case that antecedent is the parasite.

Complex sentences can and often do have more than one noun and more than one pronoun. The pronouns must be logical and must be parallel in number and gender to the noun.

It sounds as if you might believe something different. That's not accurate. I can see why you might think that were the rule, but it isn't. Answer A is correct.

Hope that helps:-)
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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
generis
robu1
As we know that all pronoun refers to the one antecedent not different one, 'it' is non underlined part refers to Schistosomiasis where as 'its' in underlined part refers to parasite. therefore A can not be right answer,???

robu , from what source did you get the rule that there can be only one pronoun that must always refer only to the main subject of the main clause?

A pronoun needs to refer to the nearest and most logical antecedent. In this case that antecedent is the parasite.

Complex sentences can and often do have more than one noun and more than one pronoun. The pronouns must be logical and must be parallel in number and gender to the noun.

It sounds as if you might believe something different. That's not accurate. I can see why you might think that were the rule, but it isn't. Answer A is correct.

Hope that helps:-)
I was just about to say the same thing, but generis beat me to it! Nice post.

generis's post is spot-on: there is no rule -- on the GMAT or in real life -- that states that you can't have multiple pronouns in a sentence, referring to different referents. In general, the GMAT wants you to pick the answer that most clearly conveys the intended meaning, and pronouns will USUALLY refer to the most recent potential antecedent. But even that isn't an absolute rule: in some cases, the GMAT tolerates some pronoun ambiguity when there are no better options available (more on that in this video. And there's definitely nothing inherently wrong with using the same pronoun twice in a complex sentence, as generis explained.

I hope this helps!
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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
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POE: 1. That Vs. Which : "that" is an essential modifier -- in other words, we wouldn't fully understand the meaning of the sentence without it -- and "which" is a non-essential modifier, meaning that it just provides some extra information.
Since, here “which” is not preceded by comma ,and it is providing essential information about the “freshwater snails” hence, “THAT” should be used. C.D & E are out.
POE 2: “IT” Vs. “Their”: Since pronoun IT & They are referring back to “a parasitic worm”, which is singular. Therefore, “IT” has to be used. B & E are out.
POE 3: Use of “THE”: The is used to be SPECIFIC about the information i.e. it is “Freshwater snails” that play host role for Parasite. Therefore usage of “The” is required. C.D & E are out.
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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
anuj04
POE: 1. That Vs. Which : "that" is an essential modifier -- in other words, we wouldn't fully understand the meaning of the sentence without it -- and "which" is a non-essential modifier, meaning that it just provides some extra information.
Since, here “which” is not preceded by comma ,and it is providing essential information about the “freshwater snails” hence, “THAT” should be used. C.D & E are out.
POE 2: “IT” Vs. “Their”: Since pronoun IT & They are referring back to “a parasitic worm”, which is singular. Therefore, “IT” has to be used. B & E are out.
POE 3: Use of “THE”: The is used to be SPECIFIC about the information i.e. it is “Freshwater snails” that play host role for Parasite. Therefore usage of “The” is required. C.D & E are out.

Hello anuj04,

That's a very interesting way of performing the PoE. Good work there.

However, I would just like to add that I would never reject an answer choice just because which is not preceded by a comma. In fact I would never reject or select an answer choice only on the basis of the usage of a particular punctuation mark.

I would find at least one deterministic error to reject answer choices. For example:

Choices B and E are incorrect for the incorrect usage of plural pronoun their to refer to singular parasite's.

Choice C is incorrect for the SV number agreement error.

Choice D is incorrect for the incorrect usage of plural life cycles because this phrase illogically suggests that the parasite has multiple life cycles.

Hope this helps.
Thanks.
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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
GMATNinja
Quote:
A. the freshwater snails that are the parasite's hosts for part of its life cycle
I don’t have a whole lot to say about (A). The first thing I notice is the modifier “that are the parasite’s hosts” – and that seems like a reasonable way to modify “the freshwater snails.”

The pronoun “its” also jumps out at me, and that would have to refer to “the parasite’s”, since that’s our nearest (and most logical) singular. And that’s fine, too: “…the freshwater snails that are the parasite’s hosts for part of [the parasite’s] life cycle…” Reasonable enough.

So I guess we’ll keep (A).

Quote:
B. the freshwater snails that are the parasite's hosts in part of their life cycle
The biggest difference between (B) and (A) is the plural pronoun “their” in (B). And that’s a problem: “their” is plural, so it has to refer to either “the freshwater snails” or “the parasite’s hosts” – and those are the same thing, anyway. So that gives us: “… the freshwater snails that are the parasite’s hosts in part of [the freshwater snails’] life cycle.”

That’s not WRONG, exactly, if you’re willing to assume that the sentence is trying to explain what happens during the snails’ life cycle. But I think that misses the point: schistosomiasis is the grammatical subject of the sentence, and the sentence is clearly trying to explain why the disease has become more common. So presumably, the sentence is interested in explaining that the snails are hosts during part of the parasite’s life cycle. The snail’s life cycle really isn’t of interest to us, and wouldn’t help explain why the parasite has become more common.

So that’s miserably subtle, but it’s basically all we’ve got, unless you want to make an unnecessarily big deal out of the prepositions. (A) is better than (B), so we can eliminate (B).

Quote:
C. freshwater snails which becomes the parasite's hosts for part of its life cycles
(C) is a little bit easier to eliminate than some of the other options. The phrase “its life cycles” really doesn’t make any sense at all: “its” presumably refers to “the parasite”, since that’s the closest (and most logical) singular noun. But then how is that “the parasite” has multiple “life cycles”? As far as I know, each parasite only has one life cycle. If not, that would be creepy AF.

There’s also a problem with the phrase “freshwater snails which becomes.” Snails are plural, so the verb would have to be “become”, not “becomes.” Plus, “which” is generally a non-restrictive modifier, so it usually follows a comma – though that’s not usually a deciding factor on GMAT questions.

So we have lots of reasons to ditch (C).

Quote:
D. freshwater snails which become the hosts of the parasite during the parasite's life cycles
(D) is a little bit better than (C)… but only a little bit.

I guess it’s nice that “its life cycles” has been changed to “the parasite’s life cycles”, but either way, it’s illogical: a singular parasite presumably has only one life cycle, not multiple “life cycles.”

It’s also nice that the subject-verb issue has been fixed (“snails… become”), but I still don’t think it’s ideal to use “which” in this type of scenario without a comma. But again: the GMAT doesn’t generally make a big deal out of comma placement, and it’s almost never a deciding factor.

And even if you ignore the comma thing, the phrase “parasite’s life cycles” is goofy enough to let us eliminate (D).

Quote:
E. parasite's hosts, freshwater snails which become their hosts during their life cycles
The plural pronoun “their” appears twice in (E), but “parasite’s” is actually singular, so “their” presumably refers to “snails.” And that’s garbage: “… freshwater snails which become [the snails’] hosts during [the snails’] life cycles…”

You could also argue that “which” needs to be preceded by a comma, as we mentioned in (C) and (D) – but again, that’s rarely a deciding factor on the GMAT.

The pronoun thing is a big deal, though. (E) is out, and we’re left with (A).

Isn't parasite's hosts plural here in option A, and why its refer to the possessive form of parasite's hosts .Pronouns don't refer to possessive forms .
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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
sandeep211986 "Its" refers to "parasite's," not "parasite's hosts," so there's no problem. (Otherwise, we are saying "The snails are the parasite's hosts for part of the parasite's hosts' life cycle," and this makes no sense. The snails host the parasite for part of the parasite's life cycle.)

Why is there no problem? First, "parasite" is singular, which fits with "its." Second, we have the possessive "parasite's," which matches nicely with the possessive "its." Third, the idea that pronouns can't refer to possessive antecedents is no longer used in GMAT SC. When I posted on this question in 2016, that "rule," also known as "possessive poison," still had some currency. We can now say that the GMAT doesn't follow this.
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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
GMATNinja DmitryFarber egmat any thoughts? thanks!
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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
crazi4ib

For your first question, that is one reason--"its" must certainly always refer to a singular noun. However, meaning matters, too. We are explaining that snails serve as a habitat during part of the parasite's life cycle. It wouldn't matter if this were only part of the snail's life cycle--that's not the meaning we want to convey.

For your second question, no, definitely not. This is partly for the reason above--its is singular, so it cannot refer to life cycles any more than it can refer to snails. Furthermore, the antecedent of a possessive pronoun (the noun that the pronoun refers back to) is not affected by what is getting possessed. Let's take a look:

If we read the sentence this way, we would replace "its" with "the life cycles'." Then the sentence would say "for part of the life cycles' life cycles." This is meaningless!

Try comparing to a simpler sentence, such as "The dog ate its breakfast." "Its" clearly has to refer to "the dog" and not "breakfast." If we allowed "its" to stand in for "breakfast," we'd be saying "The dog ate the breakfast's breakfast." ?!? We want to say "The dog ate the dog's breakfast." If it sounds odd to say "the dog" again, well, that's why we use "its"!
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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
DmitryFarber
crazi4ib

For your first question, that is one reason--"its" must certainly always refer to a singular noun. However, meaning matters, too. We are explaining that snails serve as a habitat during part of the parasite's life cycle. It wouldn't matter if this were only part of the snail's life cycle--that's not the meaning we want to convey.

For your second question, no, definitely not. This is partly for the reason above--its is singular, so it cannot refer to life cycles any more than it can refer to snails. Furthermore, the antecedent of a possessive pronoun (the noun that the pronoun refers back to) is not affected by what is getting possessed. Let's take a look:

If we read the sentence this way, we would replace "its" with "the life cycles'." Then the sentence would say "for part of the life cycles' life cycles." This is meaningless!

Try comparing to a simpler sentence, such as "The dog ate its breakfast." "Its" clearly has to refer to "the dog" and not "breakfast." If we allowed "its" to stand in for "breakfast," we'd be saying "The dog ate the breakfast's breakfast." ?!? We want to say "The dog ate the dog's breakfast." If it sounds odd to say "the dog" again, well, that's why we use "its"!

hi DmitryFarber , I read your post explaining the possessive referring to singular pronoun, and as you said, GMAT now is okay with it. And therefore, one can expect some questions related to the same.
I want to ask, can you point out some more examples or questions related to this ? I think that would really help for a non-native speaker like me to understand the concept better.
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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
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Shrey9 It's not about singular/plural. That would just be something like "its" vs. "their." The issue is that in the past, the GMAT would not allow us to use a possessive noun as the antecedent for a non-possessive pronoun, but that rule seems to have been abandoned. At its worst, it would have had us ruling out a simple sentence such as "The Beatles' producer helped them to create innovative recordings," since the intended antecedent for "them" is "Beatles" and not "Beatles'." I think the intent was to avoid more difficult/problematic usages, but in any case, I think the rule is truly gone. I don't have a list of cases, but here's one OG example that proved the GMAT had moved on:

https://gmatclub.com/forum/although-she ... 08881.html
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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
DmitryFarber
crazi4ib

For your first question, that is one reason--"its" must certainly always refer to a singular noun. However, meaning matters, too. We are explaining that snails serve as a habitat during part of the parasite's life cycle. It wouldn't matter if this were only part of the snail's life cycle--that's not the meaning we want to convey.

Thanks DmitryFarber

Re meaning: let's say answer choice A is correctly grammatically phrased such that 'snail', 'parasite' and 'host' are all singular. Do you think in that case answer choice A could be ruled out for the ambiguity as to which one 'its' refers to? I feel that even though it is more likely for the life cycles to be referring to the parasite, a correct GMAC SC answer would still avoid that potential ambiguity. Just a hypothetical thought!

And if the sentence segment was instead "the freshwater snails that are the parasite's hosts for part of their life cycles", then in that case, 'their' would refer to the freshwater snails, and the sentence would be correct even though it may have seemed less likely for the life cycles to be referring to the snails, right?
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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
crazi4ib

If we had all singular nouns, we'd still be fine. In the phrase "the freshwater snail that is the parasite's host for part of its life cycle," there's no way for "its" to refer to "host." The snail is the host for part of the host's life cycle? That doesn't make sense, since "host" itself just refers to "snail." Then, as we've discussed above, it doesn't make much sense for "its" to refer to "snail," so we're fine. However, a well-written GMAT problem won't present us with too much of a dilemma. If there's anything that the GMAT would consider ambiguous, we'll have a choice that corrects it. No choice, no worries about ambiguity. And if there's a choice that seems to correct ambiguity but isn't right, that means it has some other error. No sentence is wrong just by virtue of being too clear!

As for your second case, that would work grammatically. Would the sentence be correct? Not if that's not the intended meaning (and in this case, it apparently is not). We'd need to look at all five choices to see what was intended and decide from there.
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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
GMATNinja
Quote:
A. the freshwater snails that are the parasite's hosts for part of its life cycle
I don’t have a whole lot to say about (A). The first thing I notice is the modifier “that are the parasite’s hosts” – and that seems like a reasonable way to modify “the freshwater snails.”

The pronoun “its” also jumps out at me, and that would have to refer to “the parasite’s”, since that’s our nearest (and most logical) singular. And that’s fine, too: “…the freshwater snails that are the parasite’s hosts for part of [the parasite’s] life cycle…” Reasonable enough.

So I guess we’ll keep (A).

Quote:
B. the freshwater snails that are the parasite's hosts in part of their life cycle
The biggest difference between (B) and (A) is the plural pronoun “their” in (B). And that’s a problem: “their” is plural, so it has to refer to either “the freshwater snails” or “the parasite’s hosts” – and those are the same thing, anyway. So that gives us: “… the freshwater snails that are the parasite’s hosts in part of [the freshwater snails’] life cycle.”

That’s not WRONG, exactly, if you’re willing to assume that the sentence is trying to explain what happens during the snails’ life cycle. But I think that misses the point: schistosomiasis is the grammatical subject of the sentence, and the sentence is clearly trying to explain why the disease has become more common. So presumably, the sentence is interested in explaining that the snails are hosts during part of the parasite’s life cycle. The snail’s life cycle really isn’t of interest to us, and wouldn’t help explain why the parasite has become more common.

So that’s miserably subtle, but it’s basically all we’ve got, unless you want to make an unnecessarily big deal out of the prepositions. (A) is better than (B), so we can eliminate (B).

Quote:
C. freshwater snails which becomes the parasite's hosts for part of its life cycles
(C) is a little bit easier to eliminate than some of the other options. The phrase “its life cycles” really doesn’t make any sense at all: “its” presumably refers to “the parasite”, since that’s the closest (and most logical) singular noun. But then how is that “the parasite” has multiple “life cycles”? As far as I know, each parasite only has one life cycle. If not, that would be creepy AF.

There’s also a problem with the phrase “freshwater snails which becomes.” Snails are plural, so the verb would have to be “become”, not “becomes.” Plus, “which” is generally a non-restrictive modifier, so it usually follows a comma – though that’s not usually a deciding factor on GMAT questions.

So we have lots of reasons to ditch (C).

Quote:
D. freshwater snails which become the hosts of the parasite during the parasite's life cycles
(D) is a little bit better than (C)… but only a little bit.

I guess it’s nice that “its life cycles” has been changed to “the parasite’s life cycles”, but either way, it’s illogical: a singular parasite presumably has only one life cycle, not multiple “life cycles.”

It’s also nice that the subject-verb issue has been fixed (“snails… become”), but I still don’t think it’s ideal to use “which” in this type of scenario without a comma. But again: the GMAT doesn’t generally make a big deal out of comma placement, and it’s almost never a deciding factor.

And even if you ignore the comma thing, the phrase “parasite’s life cycles” is goofy enough to let us eliminate (D).

Quote:
E. parasite's hosts, freshwater snails which become their hosts during their life cycles
The plural pronoun “their” appears twice in (E), but “parasite’s” is actually singular, so “their” presumably refers to “snails.” And that’s garbage: “… freshwater snails which become [the snails’] hosts during [the snails’] life cycles…”

You could also argue that “which” needs to be preceded by a comma, as we mentioned in (C) and (D) – but again, that’s rarely a deciding factor on the GMAT.

The pronoun thing is a big deal, though. (E) is out, and we’re left with (A).

But in option C we have “become” as part of the choice and not “becomes”
There is no other markable difference between A and C other than “that” and “which”. Since the noun immediately preceding “that” is singular I thought of dropping A.

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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
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Quote:
But in option C we have “become” as part of the choice and not “becomes”
There is no other markable difference between A and C other than “that” and “which”. Since the noun immediately preceding “that” is singular I thought of dropping A.

Good question! First, when "that" is used as a modifier, it can describe either singular or plural entities. For example: "The shirts that Tim put in the washing machine were all clean, inspiring his daughter to give him a lengthy sermon about the evils of waste and inefficiency." Here, "shirts" is plural and it's correctly modified by "that." This is similar to the usage in (A).

If however, we were using "that" as a pronoun, in that case we'd use "those" to refer to a plural antecedent. For example, "The shirts that Tim put in the washing machine were cleaner than those he'd put in the closet." Now "those" is a stand-in for the plural noun "shirts."

The main difference between (A) and (C) is a subtle meaning issue. Consider the following:

1) "Tim hates the dogs that try to bite him."

Here, Tim only hates the dogs trying to bite him. Presumably, there are other dogs Tim doesn't hate. The "that" modifier serves to differentiate one group from another. (If you want to use fancy terminology - and you probably shouldn't - this type of modifier is "restrictive." It's necessary to understand what dog group we're talking about.)

Contrast the above with:

2) "Tim hates dogs, which try to bite him."

Now, Tim seems to hate dogs in general, and a characteristic of all dogs is that they want to maul Tim. ("Which" here is an unrestrictive modifier, meaning that it's just providing incidental information about dogs, not telling us what dogs we're discussing. And while you shouldn't spend much time worrying about comma usage, technically, we use a comma when we're introducing an unrestrictive modifier, such as "which.")

We see the same distinction here.

In (A), we have:

"...irrigation projects have enlarged the habitat of the freshwater snails that are the parasite's hosts for part of its life cycle."

The meaning here is that the irrigation projects have only enlarged the habitat of the specific snails that are hosts of the parasite. So there are other types of freshwater snails that aren't hosts and whose habitats haven't been enlarged. Makes sense.

In (C) we have:

"...irrigation projects have enlarged the habitat of freshwater snails which become the parasite's hosts for part of its life cycles."

Now the meaning seems to be that irrigation projects have enlarged the habitat of freshwater snails in general, and all freshwater snails are hosts for the parasite. It's also somewhat illogical to say "its life cycles" -- the parasite somehow has multiple life cycles? (Notice, also, that we're missing a comma before "which." One of the very rare instances when the absence of a comma is definitively wrong.)

It seems more logical to suggest that we're talking about a subset of freshwater snails having its habitat enlarged, as (A) does, than to suppose we're talking about all freshwater snails, as (C) does. (And, again, (C) is missing a necessary comma, and has a problem with a single parasite possessing multiple life cycles.)

I hope that helps!
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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
GMATNinja
Quote:
A. the freshwater snails that are the parasite's hosts for part of its life cycle
I don’t have a whole lot to say about (A). The first thing I notice is the modifier “that are the parasite’s hosts” – and that seems like a reasonable way to modify “the freshwater snails.”

The pronoun “its” also jumps out at me, and that would have to refer to “the parasite’s”, since that’s our nearest (and most logical) singular. And that’s fine, too: “…the freshwater snails that are the parasite’s hosts for part of [the parasite’s] life cycle…” Reasonable enough.

So I guess we’ll keep (A).

Quote:
B. the freshwater snails that are the parasite's hosts in part of their life cycle
The biggest difference between (B) and (A) is the plural pronoun “their” in (B). And that’s a problem: “their” is plural, so it has to refer to either “the freshwater snails” or “the parasite’s hosts” – and those are the same thing, anyway. So that gives us: “… the freshwater snails that are the parasite’s hosts in part of [the freshwater snails’] life cycle.”

That’s not WRONG, exactly, if you’re willing to assume that the sentence is trying to explain what happens during the snails’ life cycle. But I think that misses the point: schistosomiasis is the grammatical subject of the sentence, and the sentence is clearly trying to explain why the disease has become more common. So presumably, the sentence is interested in explaining that the snails are hosts during part of the parasite’s life cycle. The snail’s life cycle really isn’t of interest to us, and wouldn’t help explain why the parasite has become more common.

So that’s miserably subtle, but it’s basically all we’ve got, unless you want to make an unnecessarily big deal out of the prepositions. (A) is better than (B), so we can eliminate (B).

Quote:
C. freshwater snails which becomes the parasite's hosts for part of its life cycles
(C) is a little bit easier to eliminate than some of the other options. The phrase “its life cycles” really doesn’t make any sense at all: “its” presumably refers to “the parasite”, since that’s the closest (and most logical) singular noun. But then how is that “the parasite” has multiple “life cycles”? As far as I know, each parasite only has one life cycle. If not, that would be creepy AF.

There’s also a problem with the phrase “freshwater snails which becomes.” Snails are plural, so the verb would have to be “become”, not “becomes.” Plus, “which” is generally a non-restrictive modifier, so it usually follows a comma – though that’s not usually a deciding factor on GMAT questions.

So we have lots of reasons to ditch (C).

Quote:
D. freshwater snails which become the hosts of the parasite during the parasite's life cycles
(D) is a little bit better than (C)… but only a little bit.

I guess it’s nice that “its life cycles” has been changed to “the parasite’s life cycles”, but either way, it’s illogical: a singular parasite presumably has only one life cycle, not multiple “life cycles.”

It’s also nice that the subject-verb issue has been fixed (“snails… become”), but I still don’t think it’s ideal to use “which” in this type of scenario without a comma. But again: the GMAT doesn’t generally make a big deal out of comma placement, and it’s almost never a deciding factor.

And even if you ignore the comma thing, the phrase “parasite’s life cycles” is goofy enough to let us eliminate (D).

Quote:
E. parasite's hosts, freshwater snails which become their hosts during their life cycles
The plural pronoun “their” appears twice in (E), but “parasite’s” is actually singular, so “their” presumably refers to “snails.” And that’s garbage: “… freshwater snails which become [the snails’] hosts during [the snails’] life cycles…”

You could also argue that “which” needs to be preceded by a comma, as we mentioned in (C) and (D) – but again, that’s rarely a deciding factor on the GMAT.

The pronoun thing is a big deal, though. (E) is out, and we’re left with (A).

Does the "which" rule really not matter in GMAT? I would be very concerned if that were the case.

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Re: Schistosomiasis, a disease caused by a parasitic worm, is prevalent in [#permalink]
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