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Here is a detailed explanation to this question-
nakib77 wrote:
Fossils of the arm of a sloth found in Puerto Rico in 1991, and dated at 34 million years old, made it the earliest known mammal of the Greater Antilles islands.
(A) sloth found in Puerto Rico in 1991, and dated at 34 million years old, made it the earliest known mammal of
(B) sloth, that they found in Puerto Rico in 1991, has been dated at 34 million years old, thus making it the earliest mammal known on
(C) sloth that was found in Puerto Rico in 1991, was dated at 34 million years old, making this the earliest known mammal of
(D) sloth, found in Puerto Rico in 1991, have been dated at 34 million years old, making the sloth the earliest known mammal on
(E) sloth which, found in Puerto Rico in 1991, was dated at 34 million years old, made the sloth the earliest known mammal of
Meaning is crucial to solving this problem:Understanding the intended meaning is key to solving this question; the intended meaning of this sentence is that the fossils of the arm of a sloth that were found in Puerto Rico in 1991 have been dated at 34 million years old, and the act of dating them at this age has made the sloth the earliest known mammal on the Greater Antilles islands.
Concepts tested here: Subject-Verb Agreement + Pronouns + Meaning + Verb Forms + Modifiers + Grammatical Construction• Information that is vital to the core meaning of the sentence must not be placed between commas.
• The removal of information between commas must lead to a complete sentence.
• The "comma + which" construction is used to refer to extra information.
• The introduction of the present participle ("verb+ing"- “making” in this case) after comma generally leads to a cause-effect relationship.
A: This answer choice incorrectly places information that is vital to the core meaning of the sentence- the fact that the fossils were dated at 34 million years old - between two commas; as a result, Option A forms the clause "Fossils of the arm of a sloth...made it the earliest known mammal of the Greater Antilles islands", illogically implying that
the fossils made the sloth the earliest known mammal on the Greater Antilles islands; the intended meaning is that
the act of dating the fossils at 34 million years old made the sloth the earliest known mammal on the Greater Antilles islands; please remember, information that is vital to the core meaning of the sentence must not be placed between commas.
B: This answer choice incorrectly refers to the plural noun "Fossils" with the singular verb "has been dated". Further, Option B suffers from a pronoun error, as the pronoun "they" has no logical referent. Additionally, Option B uses the redundant phrase "thus making", leading to awkwardness and redundancy; this phrase is redundant, as "thus" can be deleted without any loss of clarity.
C: This answer choice incorrectly refers to the plural noun "Fossils" with the singular verb "was dated". Further, the removal of a phrase between commas - "was dated at 34 million years old" - leads to an incomplete sentence; remember, removing extra information between two commas should yield a complete sentence. In this sentence, the phrase "was dated at 34 million years old" between the two commas is extra information about “Fossils”; hence, removing this information must yield a complete sentence; doing so on this answer choice leads to an incomplete sentence. Additionally, Option C uses the needlessly wordy phrase "that was found", leading to awkwardness and redundancy.
D: Correct. This answer choice correctly refers to the plural noun "Fossils" with the plural verb "have been dated". Further, Option D correctly places only extra information - the fact that the fossils were found on Puerto Rico in 1991 - between commas, forming a complete sentence - "Fossils...have been dated at 34 million years old, making the sloth...islands." - that conveys the intended meaning - that the fossils of the arm of a sloth that were found in Puerto Rico in 1991 have been dated at 34 million years old, and the act of dating them at this age has made the sloth the earliest known mammal on the Greater Antilles islands; please remember, the introduction of the present participle ("verb+ing"- “making” in this case) after comma generally leads to a cause-effect relationship. Additionally, Option D avoids the pronoun error seen in Option D, as it uses no pronoun. Moreover, Option D avoids the modifier error seen in Option E, as it does not use "which". Besides, Option D is free of any awkwardness or redundancy.
E: This answer choice incorrectly refers to the plural noun "Fossils" with the singular verb "was dated". Further, Option E incorrectly places information that is vital to the core meaning of the sentence- the fact that the fossils were dated at 34 million years old - between two commas; as a result, Option E forms the clause "Fossils of the arm of a sloth...made it the earliest known mammal of the Greater Antilles islands", illogically implying that
the fossils made the sloth the earliest known mammal on the Greater Antilles islands; the intended meaning is that
the act of dating the fossils at 34 million years old made the sloth the earliest known mammal on the Greater Antilles islands; please remember, information that is vital to the core meaning of the sentence must not be placed between commas. Additionally, Option E incorrectly uses the "which + comma" construction to refer to extra information; please remember, the "comma + which" construction is used to refer to extra information.
Hence, D is the best answer choice.To understand the concept of "Extra Information Between Commas" on GMAT, you may want to watch the following video (~1 minute):
All the best!
Experts' Global Team