Here's the
official explanation provided by the GMAC for this question:
The underlined portion of the sentence cites two purposes of rehearsing a legal argument before a group of practice jurors: (1) to check whether the practice jurors understand the argument; (2) to observe their responses to the argument. The two purposes, signaled by
in order to, are best expressed by two parallel phrases conjoined by
and. The infinitive form
to observe should be paralleled by the infinitive form
to observe.
Option A: This answer choice fails because
for observation is not parallel with
to assess. For example,
observation (unlike
assess) is a noun, not a verb.
Option B: The use of the passive verb form
be assessed leads to an unnecessarily awkward sentence form—for example the juxtaposition of the conjunctions
so that and
whether. Also, this version misstates what is to be assessed, namely, the jurors’ reactions rather than
observation of those reactions. Alternatively,
observation might be absurdly read as a direct object of
understand, along with
the argument.
Option C: The verbal noun form
observing is not parallel with the infinitive verb form
to assess, and the resulting sentence is ungrammatical. The words
or not are verbiage that serves no purpose.
Option D: Correct. This version correctly conjoins two parallel phrases to express the purposes of rehearsing a legal argument. The infinitive verb-form
to assess is parallel to the form
to observe. Moreover, the noun clause
whether … argument that is the object of
assess is parallel with the noun clause
how … it that is the object of
observe.Option E: This answer choice has a failure of parallelism:
for observation is not parallel with
to assess. Purpose can be correctly expressed by
so as to, but the failure of parallelism is sufficient to make the resulting sentence incorrect
. The correct answer is D.
Please note that I'm not the author of this explanation. I'm just posting it here since I believe it can help the community.