Many groups experience polarization, which is when opinions become more and more extreme.

Many groups experience polarization, which is when opinions become more and more extreme.The statement is TRUE.
Polarization is the tendency for the dominant attitude of a group to become stronger or extreme. 
For instance, when a discussion concerning racism, members of the cluster who are racist can defend their views way more aggressively than they'd have before.

True, group polarization is when the dominant attitude of a group becomes stronger and stronger.

A, c, and d are the answers