Answer: C) prepositional phrase.
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 prepositional phrase is a phrase that begins with a preposition and ends in a noun, pronoun, or noun phrase. In the given sentence the phrase "under the bed" is a prepositional phrase, because it starts with the preposition "under" and ends with the noun "bed."