The comparison in the first part of the sentence is between the lift that hummingbirds produce and the lift that other birds produce. Thus, the second half of the comparison requires not only "other birds," but also a verb, such as "do" in the sentence as written. That eliminates choices (C) and (E), both of which compare the lift that hummingbirds produce directly to "other birds," not the lift that other birds produce.

Choice (D) also represents an incorrect comparison. "Instead of" means that one thing is done in place of another. It isn't accurate to say that hummingbirds produce more lift in place of producing the lift of other birds.

There are two differences between (A) and (B). First, the construction of the second clause is more efficient in (B), as it places "hover" and "extract" as parallel to one another. Second, "whether they be" in (A) contains an ambiguous pronoun, since "they" could refer to "hummingbirds." Choice (B) is correct.