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 brain and its development from birth to adulthood, are
• B. Neuroscientists, having amassed a wealth of knowledge about the brain and its development from birthto 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 the 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,

Answer 1

Answer: (A)

Neuroscientists, having amassed a wealth of knowledge over the past twenty years about the brain and its development from birth to adulthood, are

The noun 'Neuroscientists' is followed by a long modifier 'having amassed' and the verb comes at the end of the underlined phrase 'are'. The sentence basically means to say that neuroscientists are drawing some core conclusions based on the knowledge that they have gained. Here, let's focus on option B and C - both of these options create a parallelism when it is not needed- noun + long modifier + and + 2nd independent verb (without a first independent verb). C also adds a progressive participle, even though we are told that the action has already taken place over the past 20 years, so the tense doesn't work here. Thus, B and C are incorrect. Both D and E shift the verb to the front- 'have amassed' and turn the second half of the sentence into a participle phrase - 'now drawing solid conclusions'. There's a problem here as 'now drawing...' should modify the noun it touches (according to the modifier touch rules) and the noun it touches is 'adulthood' - 'adulthood' is 'not now drawing conclusions'. Also, there is something wrong with the tense in both these options as the verb is in the past tense and the modifying is done in the present tense. Only A comes across as grammatically sound option.