Samuel Gaertner and His Colleagues State That One Reason the Jigsaw

Samuel Gaertner and his colleagues state that one reason the jigsaw puzzle classroom is effective is that it allows the individual to develop a category of "oneness." By this he means that

A) everyone,without exception,is seen as part of a single group.
B) the individual sees him or herself as an individual separate from the group.
C) in-groups are seen as superior to out-groups,bolstering self-esteem.
D) out-groups are seen as a single,homogeneous unit separate from the in-group.