Question 28

(D) This correct choice avoids the ambiguity weakening several other choices. The correct idiomatic expression "between wolves and dogs" is utilized. Since researchers "continue to probe," an activity going on in the present, what the researchers are learning is properly in the present tense too.

In contrast,
(A) The relative pronoun "their" is ambiguous; at first the reader thinks that "their" might refer to the researchers, since the first part of the sentence is about the work of the researchers.

The verb form "has become" [present perfect tense] suggests a recently completed action. The resemblance between wolves and dogs is still a fact.

(B) The relative pronoun "their" is in a new position but is still ambiguous. "The closeness of their resemblance to wolves" is verbose and awkward. The faulty verb form "has become" is used again.

(C) The relative pronoun "them" is as ambiguous as "their", suggesting reference to the researchers. Again, the faulty verb form "has become" is used.

(E) The verb form "becomes" is now correct, but the unidiomatic "resemblance of wolves with dogs" mortally wounds this version. [Perhaps a little better: "the resemblance of dogs to wolves," but not as good as "the resemblance between dogs and wolves."]