Which of the Following Is a Limitation to Studying Fetal

Which of the following is a limitation to studying fetal alcohol syndrome (FAS) in human subjects?

A) There are not enough cases to study.
B) The studies are correlational only; one cannot assert that alcohol causes any particular effect.
C) There is very little evidence for FAS in children born to women in the United States.
D) It is impossible to obtain permission to conduct this type of research.