One Problem with Studying Identical and Fraternal Twins Raised Together

One problem with studying identical and fraternal twins raised together or apart is that

A) Often twins raised apart have very similar environments.
B) Identical twins that are raised together may be treated more similarly than fraternal twins, which could account for their greater behavioural similarity.
C) Fraternal twins may be male and female whereas identical twins are always either both male or female.
D) There is no control over the environments of twins who are raised apart.