An adverb asks: Who, What, When, Where, Why and How of a subject or action. Adverbs usually end in -ly.
With these facts we can deduct that the best identification for a verb phrase would be: slowly and carefully.
Choice A: It is wrong. It focuses on the noun and adjective rather than the adverb.
Choice B: It makes sense, but it still focuses more on the action verb rather then the adverb that is present.
Choice D: It is absurd. It is a prepositional phrase which contains no adverbs whatsoever.
Thus, Choice C: slowly and carefully, is your answer. It contains adverbs only (and a conjunction, but does not matter).
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