I am not sure why this one is vexing so many people. Perhaps many aspirants are overcomplicating matters. Keep it simple. If a shorter, just as clear option is compared side by side with one that is okay, then go for the terser answer. The GMAT™ prefers clear and concise meaning. Let us look below.
vishu1414
Although blue herons can still be found along the Maine coast, their population has declined dramatically when compared to the 1970’s, a period in which there were fewer bald eagles competing with them for food and nesting sites.
vishu1414
A)their population has declined dramatically when compared to the 1970s
The comparison is off here. We are comparing a
population to
the 1970s, rather than to another population. Keep looking.
vishu1414
B) their population has declined dramatically compared with the 1970s
Again, read this one for literal meaning, and it is comparing a
population with
the 1970s. There is no difference between
compared to or
compared with in this context, but that is beside the point.
vishu1414
C)their populations have declined dramatically since the 1970s
What is wrong with this one? The comparison is ongoing here, saying that
since the 1970s, the blue heron population has been in decline. If you are caught up on
populations versus the singular
population, think of the former as
numbers and the latter as
number. One is counting individuals, while the other is counting the whole body of animals. Either one could work. Finally, if the issue is
a period, since one might argue that
since the 1970s does not represent a distinct period, first, a period in time can be ongoing. I could say this is a post-WWII period, but I could just as easily refer to it as the period since the mid-1940s. Keep in mind, for comparison, a geological period can cover tens of millions of years. What is wrong with being in one, rather than commenting on one that has passed? Then,
a period... is nothing more than an appositive phrase, one that
can refer to the 1970s specifically, and in this case, the past tense
were in
were fewer bald eagles indicates that this latter interpretation is the correct one. If the meaning is clear and the writing is concise, then the answer is hard to argue against.
vishu1414
D) their populations have declined in comparison to those of the 1970s
E) their population has declined in comparison with that of the 1970s
I am doing something I do not typically do, grouping two answer choices together for discussion. But recall from above what I said about the population/populations split, or the compare to/compare with split. Here,
those in choice (D) logically refers back to
populations, while
that in choice (E) logically refers back to
population. It is six of one and a half dozen of the other. There is no way to separate the vital
meaning of these two answer choices. One says that
populations have declined compared to populations of the 1970s, while the other says that
the population has declined compared with the population of the 1970s. If you can get behind (E), then why not (D) as well? I like to say that if you cannot tease two answers apart, then they are both wrong. It is not that anything is grammatically incorrect about either option. It is just that they take their time to convey the vital meaning of the sentence, something that the outlier in (C) does not do.
I hope that helps. If you have a different approach, feel free to share.
- Andrew