Hi vinay1983,
You are correct!
The logic behind this type of CR prompt is fairly common on the GMAT - it's referred to as "all other things being equal" - and it means that if you focus on one idea (and study it, or change it, or manipulate it, etc.), then everything else stays the same.
In this case, you should notice that all of the studies use fruit flies in small glass containers. This assumes that everything that occurs in nature regarding a fruit fly is also going to occur in the small glass container - it assumes that "all things are equal". The scientists have deduced that small wing size is the dominate trait, but only by studying fruit flies in small glass containers. The logic demands that the scientists assume that the small glass container didn't affect the fruit flies in any discernible way. Thus, C is correct.
GMAT assassins aren't born, they're made,
Rich
