This question can get very tricky if you look at the different
parallel structures that are couched within this sentence.
The quickest way to go about it is to pick the overarching structure and check for parallelism.
In this case, the main error to look out for is
Not only X… but also Y.
Also, it’s worth remembering that on the GMAT, ‘if’ expresses a condition and ‘whether’ is used to showcase two choices.
Now let’s examine the choices:
Option A: Correct usage of ‘not only… but also…’. This option maintains the
parallelism. Let’s hold on to this.
Eliminate.Option B: This option does not maintain parallelism. ‘not only whether’ and ‘but also if’ are not parallel. Remember that ‘if’is used to state a condition and not a choice.
Eliminate.Option C: Breaks parallelism. ‘not only investigate’ is not parallel with ‘but also if’. Another error here is the use of ‘whether or not’ which on the GMAT is considered as redundant.
Eliminate.Option D: Same as C. ‘whether or not’ is redundant and there is lack of parallelism.
Eliminate.Option E: ‘not only to investigate’ and ‘but also whether’ are not parallel with each other.
Eliminate.Option A is the best choice. Hope this helps!
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Crackverbal Prep Team
www.crackverbal.com