As researchers continue to probe the highly expressive vocal and postural language of wolves,
their close resemblance to dogs has become ever more striking.
From the meaning analysis we can infer that main comparison is between
WOLVES and
DOGS, so we need to make it clear.
Verb tense used in non-underlined portion is - present simple - so we treat it as a fact, second part also requires - present simple.
(A)
their close resemblance to dogs
has become("their" - pronoun umbiguity, can refer to "researchers" and "wolves", "has become" - incorrect)(B) the closeness of
their resemblance to dogs
has become("their"- pronoun umbiguity, can refer to "researchers" and "wolves","has become" - incorrect, I don't like "closeness"
)
(C) the close resemblance between them and dogs
has become("has become" - incorrect - seems to sugest that resemblance between wolves and dogs started some time in the past, continueous now, and may be interrupted in the fututure, this is not the intended meaning, the resemplance doesn't depend on actions of the researchers)(D) the close resemblance between wolves and dogs becomes(correct idiom resemblance between X and Y)(E) the close
resemblance of wolves
with dogs becomes
(incorrect idiom - can be "resemblance between X and Y" or "resemblance to")D is the answer