Based Upon Longitudinal Studies, What Happens to Close Friendships from Preschool

Based upon longitudinal studies, what happens to close friendships from preschool through middle childhood?

A) They are relatively stable, and friendship networks tend to expand.
B) They often remain stable, but friendship networks tend to reduce in size.
C) They are generally unstable, as friendship networks tend to expand.
D) They are unstable, as friendship networks tend to reduce in size.