Marnie Is a Camp Counselor, and Her 'Troop' Has Children

Marnie is a camp counselor, and her 'troop' has children from several different racial backgrounds. She wants all of the kids to be accepting of each other despite their differences. The most effective way to accomplish this would be to

A) encourage children from different groups to play together.
B) come up with group tasks that require a cooperative effort from members of different ethnic groups.
C) give the kids a lecture on acceptance and tolerance.
D) simply allow the children to interact without intervention.