Sherif's robbers cave experiment demonstrated that prejudice and intergroup hostility can be reduced through:

The focus of Phase 3 of the Robber's Cave study was reduction of intergroup hostility.Sherif's robbers cave experiment demonstrated that prejudice and intergroup hostility can be reduced through superordinate goal, which is a task that cannot be solved by one group that requires joint effort to achieve solution.

The best sociological research method would have to be using experiments although it has some disadvantages as well

Iwould say the answer would be b