New techniques in thermal-scanning photography, a process that records

(B) is incorrect.

in greater detail, the effects of calefaction, or warming, of a river than ever before

The comparison is lost when we split .... in greater detail than ever before ...

(C) brings it together and is correct.

Techniques is plural so will take a plural verb. A and E are eliminated.
D: make possible the study (awkward construction); techniques make possible the study that it was before ?
B: than ever before should modify detail.

C

Hi GMATNinja,

Please shed some light on this question.

Thank you.

As others have noted, both (A) and (E) can be eliminated immediately because of an agreement error: "techniques" is plural, while "makes" and "has" are both singular verbs. That leaves (B), (C), and (D).

Take another look at (B): "make it possible to study, in greater detail, the effects of calcification, or warming, of a river than ever before." "Than ever before" should modify the phrase "in greater detail." The distance between these two phrases makes it difficult to understand. If you're reading the sentence for the first time, you might think, "the river is what than ever before?" (B) is out.

In (D), we have the phrase "of a river in greater detail than it ever was before." What does "it" refer to? In greater detail than the detail ever was before? In greater detail than the river ever was before? Neither interpretation makes sense. Notice that this isn't the case of an ambiguous pronoun, which is NOT a good reason to automatically eliminate an answer choice, but rather, it's a pronoun that has no logical antecedent at all. (D) is wrong.

So we're left with (C), which is the answer.

I hope that helps!

daagh
Can you evaluate my reasoning to eliminate B
"in greater detail" is separated by comma on both the side, making it a non essential modifier
That means sentence should work without it . If we remove "in greater detail", then the sentence becomes
make it possible to study, in greater detail, the effects of calefaction, or warming, of a river than ever before
we have "than" in the sentence for which there will be no comparison element . Hence choice will be incorrect
Please let me know

Thanks in Advance

Priyanka

I think it is a modifier problem in B." Than ever before" modifies 'in greater detail' but in B, they are placed far apart. Perse, 'than ever before' in B seems to describe the warming of a river.

For example, if we say that Tom's score is higher than before, we need not amplify that his previous scores were lower than the score now, as this comparison is easily understood.

the pronoun "it" is being used "before" the antecedent (to study) ? is this correct in option C?

This construction is common.
Another example in GMATPrep:
a law making it a crime to hold gold
Here, it is standing in for the portion in blue.
Conveyed meaning:
a law making to hold gold a crime

Bro have a few doubt in this question,

1. In option A and B, what is "it" referring to? Is it mandatory

2.
Option A : Option to study the effects of calefaction, or warming, of a river in greater detail
Option C : made it possible to study in greater detail than ever before the effects of calefaction,

Study is of calefaction, so shouldn't the modifier be together and hence elimiante C?



3. Option B
possible to study, in greater detail, the effects of calefaction, or warming, of a river

Analysis of option B :
a) in greater detail is between two commas making it non-essential, however it seems to be important to convey the meaning of the passage, on this basis can I eliminate B?
b) Similarly will it apply to " , or warming , "

Option C : How is the usage of "have made" correct? New technique means recently discovered and we use past perfect when saying something started in the past but continues in the present.

The "it" doesn't really refer to any concrete thing. These "non-referential" pronouns are rare on the GMAT and not worth worrying too much about, but we have seen them in OAs (here, for example). For more on non-referential pronouns, check out this thread: https://gmatclub.com/forum/for-those-wh ... l#p1829681.


I'm not 100% sure which "modifier" you're referring to, but the phrase "in greater detail than ever before" modifies "to study." This modifier doesn't NEED to touch the thing it modifies, but if anything this is a vote in favor of (C) over (A).

The prepositional phrase "of calefaction" modifies "the effects," so "the effects of calefaction" is fine in (C). And "the effects" are just the thing being studied (not a modifier), and there's no reason for it to appear immediately after "to study".

Separating "in greater detail" from "to study" in (A) is probably worse than separating "the effects" from "to study" in (C). (A) seems to suggest that the river itself was "in greater detail," and obviously that doesn't make sense.

But that's certainly not a reason to eliminate (A) right away. In general, there are no clear-cut rules defining this sort of thing, so you want to be very conservative.


When did the new techniques make it possible to study the effects in greater detail? Was it a specific moment in the past? Is it the present?

Logically, it makes a lot of sense that this was a gradual process -- using those techniques to study the effects in greater detail is something that began when the techniques came into existence (some time in the past) and continues into the present (those techniques STILL make it possible to study the effects in greater detail), so the present perfect makes sense here.

More broadly, there is some flexibility when it comes to the present perfect, and the action might not necessarily continue into the present. For example:

"Tim has taken the GMAT 8 times."

This doesn't mean that Tim is STILL taking the GMAT at the present moment. We don't know exactly when Tim took the exams, but we know that he must have taken them between some moment in the past and the present moment. So the present perfect makes sense.

The takeaway: as with most things on GMAT SC, make sure you aren't being overly rigid with the grammar "rules".

I hope that helps!

Hey, could you please clarify why 'it' is correct in C? Would be great if you provide me with some approach how to assess if 'it' is correct in these type of sentences.

It is a placeholder 'it' here.

It is possible to study 18 hrs a day.
It is possible that he complained to the manager.

'It' is a placeholder subject.

Sure, you substitute "it" with "?" (What).

So, the question you would ask is:

...have made ? possible...

Answer: to study in greater detail than ever before the effects of calefaction, or warming, of a river.

So, the above phrase (to study...a river) is the intended antecedent of "it".

The catch here is that this antecedent is used after the pronoun. However, this is quite acceptable.

p.s. Our book EducationAisle Sentence Correction Nirvana discusses this specific usage of "it". Have attached the corresponding section of the book, for your reference.

Hi ExpertsGlobal5 chetan2u,

I am still unclear on the usage of "it" in this question. I believe that "it" is used here as a placeholder and does not necessarily have an antecedent.

Please can you let me know if my understanding is correct?

Thanks in advance!

New techniques in thermal-scanning photography, a process that records radiation from surface areas, makes it possible to study the effects of calefaction, or warming, of a river in greater detail than ever before.

Option Elimination -

(A) makes it possible to study the effects of calefaction, or warming, of a river in greater detail than ever before - SV issue.

(B) make it possible to study, in greater detail, the effects of calefaction, or warming, of a river than ever before - It is not a perpetual phenomenon, so "have made" is preferred. Moreover, "than ever before" should be placed next to what "than ever before" modifies. "River"? No. "greater detail than ever before."

(C) have made it possible to study in greater detail than ever before the effects of calefaction, or warming, of a river - ok

(D) make possible the study of the effects of calefaction, or warming, of a river in greater detail than it ever was before - One issue is that the focus in option C is on the effects, but in option D, the focus has shifted to the study itself. Moreover, "than it was ever before" is redundant. The sentence before this phrase, "makes possible the study of the effects of calefaction, or warming, of a river in greater detail," already, in a way, says that we are studying in greater detail. "it" refers to "the new techniques have made the study of the effects possible" which itself is wrong as a pronoun "it" can't refer to a clause or is it a placeholder? Ambiguous.

(E) has made it more possible than ever before to study in greater detail the effects of calefaction, or warming, of a river - SV issue.