Official Explanation
3:2 split
A good way to attack sentence is to notice that we need the “auk” close to the verb “was”, in the non-underlined part. Only (C) and (D) have “auk” close to the verb “was”, so we can use a 3:2 split by looking at the very end of each answer choice. The original sentence creates too much distance between “auk” and “was”, (B) creates a nonsensical meaning.
(A) The original sentence is a little bit awkward since the "it” repeats the “auk”. The GMAT would never write a correct answer in such a way. Instead, the auk should be doing the verb. Here the verb is very far away, after the unnecessary succession of “it”s.
(B) makes it sound like the “docile nature” was driven to extinction. “As reputed by” also creates a different meaning.
(C) The second phrase, “it did not run from humans” changes the tense from the original. Also “docile” is defined as “not running from humans."
(D) Correct for something very subtle. “Docile nature” is defined as not running from humans. Therefore, we do not want to imply that docile nature and not running from humans are two separate things. By using em-dashes, (D) defines docile nature.
(E) Combines an independent clause with the verb “was”.
FAQ: What is the function of the dashes (—)?A: These are called “em dashes.” They can serve as commas, parentheses, or colons. Em dashes have multiple uses, the most common one is to "interrupt" part of a sentence, often explaining or defining something just said. That's what we have here:
...docile nature—it typically will not run from humans—
The part between the "— —" defines "docile nature."
FAQ: I thought it’s OK for verb tenses to vary when they’re in parallel structure.A: In some cases, verb tense can differ in a parallel structure for the GMAT. However, that does not mean that verb tense can differ in a way that disregards the respective temporal frames or references in question. That is, verb tense still must always agree with the temporal reference in question.
Let’s take a look at the verb tenses in answer choice C.
Because it exhibits a docile nature, it did not run away from humans, and it provided delicious meat, reputed by 19th century poachers to be delicious, the auk was nearly driven to extinction, its numbers, at one point, down to a mere thousand.
The key reason why the verb tenses cannot differ is that all of the bolded verbs refer to the same time period! Therefore, all of the verb tenses must be the same also, for the parallel structure to be maintained. If, however, we changed "exhibits" to "exhibited," then all of the verb tenses would be in agreement and, as far as parallel structure is concerned, this answer would work.
So parallelism can be maintained even when verb tenses differ. But for that to work, the verb tenses must still refer accurately to their respective time periods.