Nathan and Ethan Are Monozygotic Twins

Nathan and Ethan are monozygotic twins.However, people seldom get the two brothers mixed up because Ethan is five centimetres shorter than Nathan.What does the difference in height imply about the two brothers?

A) The two brothers have different phenotypes because Nathan is heterozygous for the "tallness" trait and Ethan is homozygous for the "tallness" trait.
B) Because the brothers display different phenotypes, they must have different alleles for height.
C) Although both brothers share the same underlying genotype, the environment has produced a difference in gene expression
D) The two brothers have different phenotypes because Ethan is heterozygous for the "tallness" trait and Nathan is homozygous for the "tallness" trait.