As researchers continue to probe the highly expressive vocal and postural language of wolves, their close resemblance to dogs has become ever more striking.
(A) their close resemblance to dogs has become (incorrect: pronoun error)
Pronoun their does not have the correct antecedent. The subject of the sentence is researchers thus pronoun their means researchers' resemblance that is incorrect)
(B) the closeness of their resemblance to dogs has become (incorrect: pronoun error)
The same as option A has
(C) the close resemblance between them and dogs has become (incorrect: pronoun error)
Them again denote researchers and meaning will be researchers and dogs have become.
(D) the close resemblance between wolves and dogs becomes (the best option)
It does not have any pronoun error and it follows the parallelism of as x, y (as x, as y in which second is as is omitted )
(E) the close resemblance of wolves with dogs becomes (incorrect: meaning error)
Resemblance with dogs is incorrect. The intention of the passage is to both resemblances instead of resemble of one.