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