Answer: C) Ten o'clock.
Explanation: a preposition is a word governing, and usually preceding, a noun or pronoun and expressing a relation to another word or element in the clause. A preposition is often followed by a noun, pronoun and/or modifiers, that can represent the object of the preposition. In the given sentence, the preposition is "at" and the object of that preposition is "ten o'clock" in this case there aren't any modifiers.
