I think this one is pretty tough, and it's another good example of the fact that pronoun ambiguity isn't an absolute rule on the GMAT. For more on this question, check out the video of our YouTube live session
here.
Quote:
(A) rather than burning calories to generate it
On the face of things, it looks like "it' is ambiguous, because it could refer to "the Sun" or "their body heat." But again, pronoun ambiguity isn't an absolute rule, and the more important thing is the comparison: "by
drawing their body heat from the Sun rather than
burning calories..." Hey, that looks pretty good. Let's keep (A), just to be safe.
Quote:
(B) rather than the generation of body heat by burning calories
Now the comparison is a mess. Comparisons need to be both parallel and logically sound, and this one is neither of those things: "by
drawing their body heat from the Sun rather than
the generation of body heat by burning calories..." Eliminate (B).
Quote:
(C) and not from generating it by burning calories
The parallelism is a hot mess here, too. "Not from generating it..." follows the parallelism marker "and." What's parallel to "not from generating it"? Structurally, our only real option is "from the Sun."
But wait: that makes no sense at all. "Reptiles, by drawing their body heat... and (not) from generating it by burning calories." That really doesn't work. (C) is gone.
Quote:
(D) instead of by burning calories for generating it
This one isn't terribly different from (A), but the few little differences are a problem. "Burning calories
for generating it" isn't quite the right idiom -- I think we'd prefer "burning calories
to generate it", as in (A). I'm also really not sure that the "by" is necessary here. More importantly: the GMAT seems to prefer "rather than" over "instead of." (And we could launch into a long discussion of that one, but GMAT Club threads on this topic can be found
here and
here.)
So (D) can be eliminated.
Quote:
(E) instead of body heat generated by burning calories
The comparison is messy here again: "by
drawing their body heat directly from the Sun instead of
body heat generated by burning calories"... that's a mess. Plus, we still have the "instead of" problem.
So (E) is gone, and (A) is the winner. Again, the "it" might feel ambiguous in (A), but pronoun ambiguity is not an absolute rule on the GMAT -- and the logic of the comparison is far more important.