Answer:
a. homogeneous, practically like clones of each other
Step-by-step explanation:
In social psychology and sociology, an in-group is the social group where a person psychologically identifies him as being a member of the same group. Where as in an out-group, individuals do not identify and belongs to the same group.
In group refers to similar features or homogeneous or belonging to the same group.
In the context, the rebels finds the defender of the empire or the soldiers of the empire as an in-group, because they belong to the same planet or place. They are like clones to each other and are homogeneous.
Hence the correct option is (a).