Hey Charu,

I have doubts about this question. Let's start by looking at the conclusion/premise:

Conclusion: Today's flightless birds developed their feathers to manage body temp
Premise: Ancient reptiles developed their feathers to manage body temp, and many couldn't fly

The argument seems to be assuming that just because ancient reptiles had one characteristic in common with some of today's birds (can't fly), they must have another characteristic in common (feathers for body temp regulation).

(A) is the best answer. The argument would go that birds may have developed their feathers to fly, then lost the ability to fly. If (A) is true, then the feathers would have gone away, so they couldn't have developed for flight, which means they must have developed for something else, such as managing body temperature.

My problem with this answer is that we have no evidence that birds originally developed feathers to fly. If we assume they developed feathers for the same reason that reptiles did (insulation), then they never LOST the ability (to regulate their body temperature), so (A) is irrelevant. In short, this is the best answer, but I REALLY wish the stimulus included the sentence "Birds originally developed feathers in order to fly."

(B) is irrelevant. We care about the body temp regulation issue, not flight.

(C) is also irrelevant. We're making a connection between flightless reptiles and flightless birds. A fact about feathered dinosaurs that can fly doesn't matter to us.

(D) is out of scope. The argument doesn't ever discuss the genetic issue. If anything, assuming this kinda renders the argument pointless, because if the birds are direct descendants, they didn't really develop their feathers as a SEPARATE development.

(E) is way too strong. Just because flightless birds haven't gone extinct yet doesn't prove that they're using their feathers to manage body temperature. They could be doing it with some other aspect of their physiology.

Hope that helps!

-t