In order to manage, protect, and control territory locally, a country often
a. divides into administrative units
b. establishes an enclave
c. establishes an exclave
d. creates an autonomous region

Enclave and exclave are definitely not the correct answer : they are part of a country not directly joined with the mainland and don't have anything to do with  controlling it.

Both other options are actually correct but an autonomous region is much more than just a way to control territory locally - it also implies that the region has a  kind of independence.

Therefore the best answer is a.  divides into administrative units