The clause in the sentence that is an adverb clause is C.after you clean your room.
Adverb clauses, or adverbial clauses, are dependent clauses that function as adverbs, so they give more information about the action. Since they are dependent clauses, they are usually introduced by a subordinating conjunction to connect it to the main sentence. Moreover, as they are clauses, these contain both subject and predicate.
In this case, after is the subordinating conjunction that introduce the new subject and verb, that make up the dependent clause. This clause is modifyinh the verb visit.