The Conclusion to Be Drawn in Studies of Adopted Children

The conclusion to be drawn in studies of adopted children is that

A) both genetic and environmental influences play a role in the development of intelligence.
B) the level of intelligence an individual attains is due primarily to genetic factors.
C) the level of intelligence an individual attains is due primarily to environmental factors.
D) biological mothers of adopted children tend to have, on average, lower IQs than other mothers.