The correct answer is C.
An exclave is a territory which pertains to a certain country but that is physically separated from its main territory and, alternatively, it is completely surrounded by the territory of a different country.
The main reason to maintain such exclaves is either to conduct economic or military strategies. For example, in the case of Gibraltar, the United Kingdom maintains this small of territory located in the Mediterranean Sea, which is very useful for trade routes and for preparing and releasing military operations towards Africa or the Middle East.
