The answer is: [C]: a preposition followed by a noun, pronoun, or phrase.
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Note: Answer choice "A" is incorrect.
A 'prepositional phrase' ALWAYS begins with a preposition.
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Answer choice "B" is incorrect. A 'prepositional phrase' does, in fact, always, start with a preposition, but does not HAVE to be followed by ONLY a [noun or pronoun].
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