Identical twins have almost all of their genes in common, so any _____ between them is in large part due to the effects of the environment.
(A) adoption
(B) familiarity
(C) stability
(D) variation

同卵雙胞胎的幾乎所有基因都是共同的，因此它們之間的任何變異在很大程度上都歸因於環境的影響。