The main function of an acropolis was to provide a) housing for wealthy merchants b) land for growing crops that would be used for trade c) protection from attacks d) a central marketplace and public square

Acropolis means 'high city' in Greek.

Most city-states in ancient Greece had at their center on a rocky mound or hill where they built their important temples and where the people could retreat to if under attack. ...

The Athenian Acropolis is home to one of the most famous buildings in the world: the Parthenon.

so your answer would logically be: C

Hope this helps:)