Cohesiveness of a group will increase if:

a. the group hasn't experienced prior successes.
b. admission into the group is more difficult to obtain due to various barriers or high criteria.
c. members perceive that an internal force may prohibit the group from obtaining its goals.

b. admission into the group is more difficult to obtain due to various barriers or high criteria.    

Explanation:

Group cohesion: In social psychology, the term "group cohesion" is described as one of the different social processes that distinguish different groups whose members tend to interact with each other and signifies forces that push these group members intact with each other. However, a lot of people are working together in a group to accomplish a specific task and experiences bad as well as a good experience.

In the question above, the correct answer is b.

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