In a Study That Compared Twins to Unrelated Pairs of Students

In a study that compared twins to unrelated pairs of students, who were the same age and sex, the unrelated pairs of students were almost as alike as the twins. These unrelated pairs had similar political beliefs, musical interests, religious preferences, job histories, hobbies, and favorite foods. These unrelated students were so similar because

A) the students in the study actually were similar in their genetic make-up.
B) they were selected through procedures that were biased in favor of the middle class.
C) they were of the same age and sex, living in the same historical times, and selecting from similar societal options.
D) the pairs of twins were so dissimilar that the unrelated pairs of students appeared very similar to each other in comparison.