In many species of Drosophila, flies of any genotype that are reared in a cold environment tend to be larger than flies of the same genotype raised in a warm environment. Is this an adaptation?

A) Yes, because phenotypic plasticity is always adaptive.
B) Yes, but only if there is evidence of allometry.
C) Maybe, but confirming this would require further experiments examining survival and reproduction of different sized flies.
D) Maybe, but confirming this would require further experiments examining whether the differences in size are genetic.