The bowerbirds of Australia derive their name from the fact

OA is B

The original sentence contains the pronoun "them" but it is not grammatically clear whether the pronoun's antecedent is "bowers of sticks and twigs" or "females." Logically, we know that the antecedent is "bowers", so we need to find a replacement that makes this clear. Moreover, the bowerbird does not derive its name from the fact that it builds bowers, but from the bowers themselves.

(A) This choice is incorrect as it is the same as the original sentence.

(B) CORRECT. This choice rewrites the sentence to make it clear that the name derives from the bowers and not from the fact of building them, and it also eliminates the pronoun "them" and instead refers to "structures" to make the relationship clear.

(C) This choice does not make it clear that the males build the bowers and decorate them. Instead, it seems to suggest that the bowers exist on their own and that the male uses only the flowers and vegetation to attract females.

(D) This choice uses the phrase "having decorated them" improperly. It is not necessary to use "having" in this context because the sentence describes an ongoing event, not one that occurred in the past.

(E) This choice is in the passive voice, which is not preferable to active voice when a grammatical active version (such as B) is also offered. Moreover, the choice implies that the males only build the bowers. Since the original sentence clearly indicates that the males also decorate the bowers, this choice changes the meaning unacceptably.