Adjective clauses usually start with the words: that, when, where, who, whom,whose, which, and why. also it's function as an adjective answers the questions "what kind?", "how many?" or "which one?"
SO the answer is A, because it uses the word which, and answers the question "which one?"
Answer:
I aced my test because I remembered to study. The complete subordinate clause is: because I remembered to study.
Explanation: