Claude Bouchard Conducted Research on the Effects of Overfeeding on Weight

Claude Bouchard conducted research on the effects of overfeeding on weight gain and found that identical twins have similar weights regardless of whether they are raised together or apart.This study provides evidence for the idea that

A) environment plays an important role in weight gain.
B) being an identical twin is stressful and therefore likely to cause weight gain.
C) weight gain is inevitable for most people if they overeat.
D) genes play an important role in weight gain.