Question: Neuroscientists, having amassed a wealth of knowledge over the past twenty years about the brain and its development from birth to adulthood, are now drawing solid conclusions about how the human brain grows and how babies acquire language.

(A) Neuroscientists, having amassed a wealth of knowledge over the past twenty years about the human brain and its development from birth to adulthood, are
(B) Neuroscientists, having amassed a wealth of knowledge about the brain and its development from birth to adulthood over the past twenty years, and are
(C) Neuroscientists amassing a wealth of knowledge about the brain and its development from birth to adulthood over the past twenty years, and are
(D) Neuroscientists have amassed a wealth of knowledge over past twenty years about the brain and its development from birth to adulthood,
(E) Neuroscientists have amassed, over the past twenty years, a wealth of knowledge about the brain and its development from birth to adulthood,

Correct Answer: A
Explanation: Neuroscientists, having amassed a wealth of knowledge over the past twenty years about the human brain and its development from birth to adulthood, are.- Correct. This answer choice acts upon the subject - "Neuroscientists" - with the independent verb "are now drawing" to form a complete thought, leading to a complete sentence. Further, it uses the phrases "having amassed a wealth of knowledge over the past twenty years" and "are now drawing". Conveying the intended meaning - that over the past twenty years. Neuroscientists have amassed a wealth of knowledge about the development the human brain undergoes from birth to adulthood. And as a separate action, they are now drawing solid conclusions about how the human brain grows and how babies acquire language. Let’s take a look at the other choices.

Option B
Neuroscientists, having amassed a wealth of knowledge about the brain and its development from birth to adulthood over the past twenty years, and are. Incorrect.
1) The phrase “over the past twenty years” seems to talk about the development of the brain from birth to adulthood that took twenty years to develop. However, it is the neuroscientists who took twenty years to study about the development of the brain. Thus, this choice distorts the meaning of the sentence.
2) The clause preceding conjunction “and” does not have a main verb. Thus this choice is a fragment.

Option C
Neuroscientists amassing a wealth of knowledge about the brain and its development from birth to adulthood over the past twenty years, and are.- Incorrect. This answer choice fails to form a complete sentence. "amassing" is a present participle acting as a noun modifier, and "are now drawing" is part of a dependent clause. Meaning there is no independent verb to act upon the subject - "Neuroscientists". It further alters the meaning of the sentence through the phrase "development from birth to adulthood over the past twenty years". The construction of this phrase incorrectly implies that over an unspecified amount of time. Neuroscientists have amassed a wealth of knowledge about the development the human brain underwent over the past twenty years. Specifically, from birth to adulthood; the intended meaning is that over the past twenty years. Neuroscientists have amassed a wealth of knowledge about the development the human brain undergoes from birth to adulthood.

Option D
Neuroscientists have amassed a wealth of knowledge over past twenty years about the brain and its development from birth to adulthood,- Incorrect.
1) The phrase “over the past twenty years” seems to talk about the development of the brain from birth to adulthood that took twenty years to develop. However, it is the neuroscientists who took twenty years to study about the development of the brain. Thus, this choice distorts the meaning of the sentence.
2) The clause preceding conjunction “and” does not have a main verb. Thus this choice is a fragment.

Option E
Neuroscientists have amassed, over the past twenty years, a wealth of knowledge about the brain and its development from birth to adulthood- Incorrect. In this choice, just like choice D, the second clause preceded by comma does not have a main verb making it a fragment. Generally, a clause is introduced after the comma. But here, there is neither any subject nor any verb for the clause. Moreover, the clause is a fragment. Also, the modifier “now drawing” seems to modify “adulthood” which makes no sense.

“Neuroscientists, having amassed a wealth of knowledge over the past”- is a GMAT sentence correction question. These sorts of questions come up with grammatical errors in the underlined part of the sentence. The candidates need to select the correct statement given in the options. The GMAT sentence correction section demands good skills in grammar since the candidate has to identify common grammatical errors. GMAT sentence correction is a part of GMAT verbal.

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