Federal authorities involved in the investigation have found the local witnesses are difficult to locate, reticent, and are suspicious of strangers.

(A) the local witnesses are difficult to locate, reticent, and are
(B) local witnesses to be difficult to locate, reticent, and are
(C) that local witnesses are difficult to locate, reticent, and
(D) local witnesses are difficult to locate and reticent, and they are
(E) that local witnesses are difficult to locate and reticent, and they are

I'd go with C as well.

The "they" after "and" is unclear as referring to the local witnesses or federal authorities and so options D and E are out. Of the remaining, C is better construct as per parallelism rule that everything after the second item should sound like the second item. Infact, all the three items here are qualifying the local witnesses. So, the first item in the list of parallels is independent. B and A also cause tense issues because of an "are" after the "and", if you read properly.
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D and E are grammatically structure wise correct but meaning wise not.

Difficult (adjective ) to locate (verb)
Reticent (adjective)
Suspicious (adjective) of strangers.


Therefore difficult to locate and reticent is not correct; one must be aware of the meaning of reticent; if one considered it as a verb then one will end up picking D or E ... E is better over D.

C is right, bit tricky question exploiting vocabulary.
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Hi , I have a doubt, can we use "," before AND?

if we are using ",and " then a verb must follow..like it is given in D??
can someone please explain the correct ", and" usage
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Hi,
Let me try

Federal authorities involved in the investigation have found the local witnesses are difficult to locate, reticent, and are suspicious of strangers.


(C) that local witnesses
are difficult to locate,
(are) reticent,
and
(are) suspicious of strangers

we don't need to repeat the 'are' in the above list.


Hope it helps.

Find needs "that" to be grammatically correct which leaves us with 2 options.
Option E unnecessarily uses "they" making it more ambiguous hence answer option C.

Total time taken to mark correct answer : 9 seconds.
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Typically, when you have a pronoun as the subject of a clause, the most logical place to look for a referent is the subject of the previous clause. In (E), the subject of the first clause is "federal authorities." It certainly wouldn't make any sense to claim that it's the federal authorities who are suspicious of strangers, rather than the local witnesses. So the issue here isn't pronoun ambiguity, but rather, the illogical meaning created by the pronoun. (And it's true that pronoun ambiguity isn't an absolute rule on the GMAT. More on that in this video.)

As for the parallelism, take another look at (C). "Federal authorities involved in the investigation have found that local witnesses are difficult to locate, reticent, and suspicious of strangers." The parallel elements in red are all adjectives describing the witnesses. It's fine that two of those adjectives are themselves modified by the parts in blue - there's no grammar rule that says that all elements of a list have to look exactly the same. They just have to perform the same function. Here they all describe the "witnesses," so there's no problem.

I hope that helps!
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