Barbara and Brenda Are Identical Twins Who Were Adopted at Birth

Multiple Choice

Barbara and Brenda are identical twins who were adopted at birth and raised by two different families. Andy and Andrew are identical twins raised together by their biological parents. When the four children entered high school they took an IQ test. Barbara and Andy each had scores of 110, while Brenda's IQ was measured at 120 and Andrew scored 108. These results support which of the following conclusions?

A) Intelligence is influenced by the environment only in extreme conditions
B) Intelligence is almost entirely shaped by the environment except when rare genetic disorders are involved
C) Intelligence is shaped by genetics as well as environmental influences
D) Intelligence is entirely determined by genetics