In a Typical "Boundary Violation" Between Children's Play Groups in Middle

In a typical "boundary violation" between children's play groups in middle childhood,

A) best-friend pairs terminate their friendship bonds and re-form into new groups of friends.
B) a child will be accepted into a play and friendship group of children of the other gender for an extended period of time.
C) a girl will exit her friendship group as a result of a quarrel or hurt feelings.
D) a brief interaction, such as a "chasing game," will cause one gender-segregated group to breach the barrier of the other gender-segregated group.