Answer: C) who has dark red hair and sits in the front row.
Explanation: A subordinate clause is a phrase that doesn't make complete sense on its own, it needs to be joined to an independent clause (which make complete sense by itself). In the given sentence the independent clause is "The boy did well on the test" and the subordinate or dependent clause is "who has dark red hair and sits in the front row" notice that if we remove the subordinate clause, the meaning of the sentence stays the same.
