The Coast Guard recently redesigned channel markers in the Chesapeake

First of all, usage of "numbers of" is not incorrect when used by itself. However when used with "A numbers of" or "THE numbers of", it is incorrect.
In option B, "their huge nests" is an independent clause and therefore must be preceded by a conjunction. This is a run on sentence and hence incorrect.
In option C, use of amounts is incorrect. Amount is used for uncountable nouns and since ospreys can be counted, it's wrong. Also "the huge nests of which.." is wordy. This is also wrong.
In option D, "nests of ospreys they" is awkward and unidiomatic.
In option E, introduction of an independent clause starting with "and" is unnecessary and fails to convey the meaning properly.
Option A is grammatically correct."Whose" correctly refers to "ospreys". This should be the answer.

(A) whose huge nests correctly modifies ospreys. Keep it.
(B) 'Their huge nests' has ambiguous antecedent. It could be Coast Guard or ospreys. Eliminated.
(C) The modifier 'which' is far away from what it modifying. Also, which is used not non living things. Eliminated.
(D) Clearly incorrect.
(E) Here, Emphasis is on 'and' which distorts the meaning of the sentence.

IMO, Option A.

The Coast Guard recently redesigned channel markers in the Chesapeake Bay to accommodate large numbers of ospreys, whose huge nests formerly obstructed the lights.


(A) numbers of ospreys, whose huge nests
(B) numbers of ospreys, their huge nests
(C) amounts of ospreys, the huge nests of which
(D) nests of ospreys they
(E) numbers of ospreys, and their huge nests

ospreys appear to be countable; therefore, amount is incorrect. Eliminate (C)
(E) fails at parallelism both side of "and" does not have a similar structure
(D) they is not clear which plural noun it refers to

(A) and (B)
(B) has two independent clauses without proper conjunction or semicolon

Ans: (A)

The Coast Guard recently redesigned channel markers in the Chesapeake Bay to accommodate large numbers of ospreys, whose huge nests formerly obstructed the lights.


(A) numbers of ospreys, whose huge nests --> the best answer choice. "whose" is a good choice since nests are ospreys'.
(B) numbers of ospreys, their huge nests --> run-on sentence
(C) amounts of ospreys, the huge nests of which --> ospreys are countable. Therefore, "amounts" is not right.
(D) nests of ospreys they --> what obstructed the lights was large numbers of ospreys and their nests, not large nests.
(E) numbers of ospreys, and their huge nests --> The Coast Guard redesigned...and their huge nests obstructed... --> this sounds like "because of the redesign, their huge nests obstructed.." Actually, the meaning is exactly opposite.

Official Explanation :

Choice B and D are run on sentences.

In choice C, the use of “amount” is incorrect since “ospreys” is a countable noun.

Choice E distorts the meaning.

Hence, A is the best choice.

Dear Friends,

Here is a detailed explanation to this question-


Choice A: This answer choice uses the appropriate term "number" to refer to the countable noun "ospreys", preserves the intended meaning of the sentence, and properly links the independent and dependent clauses through a comma. Thus, this answer choice is correct.

Choice B: This answer choice links two independent clauses with a comma, leading to a comma splice error. Thus this answer choice is incorrect.

Choice C: This answer choice uses the word "amounts" to refer to the countable noun "ospreys". Thus, this answer choice is incorrect.

Choice D: This answer choice changes the meaning of the sentence to imply that the Coast Guard took action to accommodate only the nests of ospreys, rather than to accommodate the ospreys themselves. Additionally, this answer choice fails to provide conjunction or appropriate punctuation between two independent clauses. Thus, this answer choice is incorrect.

Choice E: This answer choice alters the meaning of the sentence to imply that the Coast Guard took action to accommodate the ospreys and, unrelatedly, the ospreys' nests formerly obstructed the lights. Thus, this answer choice is incorrect.

Hence, A is the best answer choice.

To understand the concept of "Comma Splice and Run-ons on GMAT", you may want to watch the following video (~6 minutes):



To understand the concept of "Collective, Countable, and Uncountable Nouns on GMAT", you may want to watch the following video (~ 2 minutes):



All the best!
Experts' Global Team

EASY, COUNTABLE MODIFIERS



The Coast Guard recently redesigned channel markers in the Chesapeake Bay to accommodate large numbers of ospreys, whose huge nests formerly obstructed the lights.



(A) numbers of ospreys, whose huge nests ------ CORRECT


(B) numbers of ospreys, their huge nests ----- Run on sentence. They place the clause "nests obstructed" but do not connect it to the first clause.


(C) amounts of ospreys, the huge nests of which ------- "Amounts" is wrong, since "ospreys" is a countable noun.


(D) nests of ospreys they ------- run on sentence. They place the clause "nests obstructed" but do not connect it to the first clause. Additionally this sentence changes the meaning, as it implies that the nests are large, and not that their number is large.


(E) numbers of ospreys, and their huge nests ------ This sentence changes the meaning as it creates parallelism between to main clauses "coast guard redesign" and "nests obstructed" that do not have a logical connection.

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