Pretty sure it's C. while that's what i'd go with, it could be B.
<span>A. prepositional phrase </span>
Answer: professional
Explanation:
The opposite of amateur is professional
The parts of speech are the category to which a word is assigned based on its context and use in a sentence. The main categories consist of noun, pronoun, adjective, determiner, verb, adverb, preposition, conjunction, and interjection.