Which of the following definitions best describes an enclave?
A. a separate part of a city dedicated largely to one group
B. an industrial neighborhood in a manufacturing zone
C. an area around a city that has not been influenced by immigrants
D. a region of a city that was established as off-limits to immigrants
.

Option-A

Explanation:

The grammatical meaning of the enclave refers to the portion of the territory which is surrounded by a large territory. The enclave in a city refers to the enclosed area of a territory which has people of a particular cultural and societal status.

There are few cities which are also considered as enclaves like San Marino or the Vatican city-state which are surrounded by the territory of Italy.

Thus, Option-A is correct.

separation of church and state? not sure what you mean.