According to Social Identity Theory,why Do People Display Ingroup Favouritism

According to social identity theory,why do people display ingroup favouritism?

A) They use it as a way of displacing negative feelings toward the outgroup.
B) They use it as a means of increasing self-esteem.
C) They use it because they expect to be treated unfairly by outgroup members.
D) They use it because intergroup competition demands it.