What were the crusades? a. battles at sea involving a special type of ship sailing from constantinople b. wars between christians and muslims over control of the holy land c. efforts by the pope to get everyone to contribute money to the church d. the crosses that decorated the breastplates of certain knights

The correct answer is C.

A is incorrect because the battles were not at sea and had nothing to do with ships.
C is incorrect because the Crusades had nothing to do with contributing money to the Church (but rather defending it against Muslims).
D is incorrect because, although knights did wear these crosses, they, alone, were not the Crusades.