One of the Criticisms That Has Been Leveled at Research

One of the criticisms that has been leveled at research that examines the similarity between twins separated at birth is that

A) there are so few cases of separated twins that this research cannot really tell us very much about the relative influence of genetics and environment.
B) in many cases the twins were not really separated because they were adopted by relatives or lived close to each other while growing up.
C) we do not yet have statistical techniques that allow us to separate the effect of genetics from the effect of the environment.
D) many of the reports of great similarity between separated twins has been exaggerated and these reports are not supported by data.