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11 Mar 2021, 21:52
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Patilsv28
Referring to choice (B), "that blocked shad from migrating up their spawning streams" is one big ol' modifier. And what does it modify? Well, what would block shad from migrating up their spawning streams? I'm no expert on milldams and culverts, but they sound like things that could block the fish (a milldam is a type of dam, right?). "Overfishing" certainly wouldn't block the fish, nor would the proliferation itself.
So, given the context, the clause "that blocked shad from migrating up their spawning streams" modifies the nouns "milldams and culverts." If you like jargon: the relative pronoun "that" technically serves as the subject of the clause, and "blocked" is the corresponding verb.
Note that if this verb had been in the past perfect ("had blocked"), the reader would wonder about the timing of this action in relation to other past actions: did the action of blocking shad migrations only happen before 1920 or only before landings were reduced?
By using the simple past ("blocked"), the timing of this action is not limited to specific parts of the timeline in the past -- it's simply what the milldams and culverts did (past tense) once they were built. The more milldams and culverts that were built, the more the shad migrations were blocked. And that blocking of the shad migrations reduced landings over time.
Let's take another look at choice (B), this time omitting the noun modifier:
- "... by 1920, over-fishing and the proliferation of milldams and culverts had reduced landings to less than four million pounds."
Here, the use of the past perfect ("had reduced") makes perfect sense with the time marker ("by 1920"), making it clear that "over-fishing and the proliferation of milldams and culverts... HAD reduced landings to less than four million pounds" BY 1920.
I hope that answers your question!
07 Apr 2021, 20:11
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UNSTOPPABLE12
I wouldn't automatically assume that the "having..." part modifies "proliferation" instead of "milldams and culverts" just because it isn't separated by commas. But I would agree that the reader could interpret the "having..." part as a modifier for the entire clause ("over-fishing and the proliferation reduced landings") -- and that interpretation wouldn't make any sense.
As with most things SC, you want to think about meaning instead of trying to arrive at the right answer by blindly applying a set of formulaic "rules." Even if the "having..." part were separated by commas, I don't think (D) would be much better. Notice that using "having blocked shad from migrating up their spawning streams" seems to separate this action (blocking shad) from the action of reducing landings. In other words, it sounds as though the milldams and culverts completed the action of blocking the shad and then, at some point after having blocked the shad, the milldams and culverts reduced landings.
But that's not quite right. These two actions occurred at the same time. As explained in this post, the blocking of the shad migrations reduced landings over time.
So it's not that the "having..." is clearly wrong because it violates some set of rigid rules. It's just that the use of "that" in (B) makes the logical meaning clearer. (For those just joining the thread, this is one of the two reasons for picking (B) over (D) that we discussed in an earlier post.)
As much as we'd love to boil SC down to an easy-to-memorize algorithm based on grammar rules, it simply doesn't work that way. Every question is different, and you always have to think carefully about meaning -- and that's hard work, sadly.
I hope that helps!
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29 Apr 2021, 03:40
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Hi EducationAisle
In option "A" and "B" why is B preferred over "A"? as we already know present perfect tense can logically substitute a past tense, when it is used as a time marker for past perfect tense.
All I could reckon from that rule was "present perfect tense" can replace "past tense" in cases where 1) An event happened from now to infinitely in the past 2) An event from now till some time bracket in the past, whereas it won't replace past tense 3) in an event where present-perfect is used to refer something that started in the past and is continuing till now in present, something like we talk about in "Since" sentences.
We don't have construct (3) here.
In option "A" and "B" why is B preferred over "A"? as we already know present perfect tense can logically substitute a past tense, when it is used as a time marker for past perfect tense.
All I could reckon from that rule was "present perfect tense" can replace "past tense" in cases where 1) An event happened from now to infinitely in the past 2) An event from now till some time bracket in the past, whereas it won't replace past tense 3) in an event where present-perfect is used to refer something that started in the past and is continuing till now in present, something like we talk about in "Since" sentences.
We don't have construct (3) here.
). If we were counting the number of fish, we'd say "fewer": "fewer than four million fish." 
