Answer:
who bought me a soda
Step-by-step explanation:
Adjective clauses are groups of words consisting of at least a subject and a verb and whose function is to modify or describe nouns. They tend to begin with a relative pronoun (who, whom, whose, that, which) or a relative adverb (when, where, why) which can be the subject of the clause. “who bought me a soda,” then, is an adjective clause because it describes or gives us information about the noun “the guy” and it also has a subject (in this case, “who” and a verb (“bought”).