Starfish, with anywhere from five to eight arms, have a strong regener

So there’s an interesting thing in this question: “starfish” could, in theory, be either singular or plural. (Much like the word “media” or “data” or “deer” or diabetes.) The GMAT has a very consistent habit in these cases: the sentence will always give you some other indication of whether the word is singular or plural.

This is awfully tempting, and I don’t think that there are any DEFINITE reasons to prefer (E) over (B). But there are a bunch of things that make (B) very, very slightly better.

Let’s line this one up with (B) to make it easier to compare them:

(B) one arm is lost it is quickly replaced, with the animal sometimes overcompensating and
(E) they lose one arm it is quickly replaced, sometimes with the animal overcompensating,

So we have three meaningful differences here, and none of them are smoking guns, but all of them seem to point in the same direction.

In that first chunk of the sentence, the big difference is that (E) uses the pronoun “they”, which is potentially ambiguous, since it could refer back to “starfish” or “arms” – and since “arms” is the most recent plural, you could argue that “they” is a legit problem here. Honestly, I’m not completely convinced by this – there are plenty of official SC questions with similar ambiguities in the correct answers. But in this case, the pronoun issue gives me a very slight preference for (B).

Second, we have some funny business with the placement of the word “sometimes.” The thing that “sometimes” happens is “overcompensating”, so it makes sense to have “sometimes” right next to that word. Is it totally wrong to say “sometimes with the animal overcompensating”? Nope. But again, I’d have a very slight preference for (B) based on the placement of “sometimes.”

And the third thing? In (B), “overcompensating” and “growing” are two parallel actions. In other words, the animal sometimes does two things: it overcompensates and grows an extra arm or two. That makes enough sense. In (E), “growing” has been turned into a modifier (“sometimes with the animal overcompensating, growing an extra arm or two”), and I’m not sure that it’s wrong, but it seems a little bit odd to me: when do you ever see an "-ing" participle modifying another "-ing" participle? Meaning-wise, I suppose you could argue that “growing” tells us extra information about when happens when the animal is “overcompensating”, but I think it makes more sense to keep the two actions (“growing” and “overcompensating”) parallel.

Honestly, I don’t think that any of these three issues are crystal-clear, slam-dunk reasons to eliminate (E). If I were seeing this question on an actual exam for the very first time, I’d say a quick prayer to the GMAT gods before picking (B) and moving on -- but at least I'd be comforted by the notion that all three of those little issues point in half-assed unison toward (B).