The answer to your question would be that in the selected group of words there is one subordinate clause only. That is, the correct option would be D.
A subordinte clause, also known as dependent clause, will begin with a subordinate conjunction or a relative pronoun and will contain both a subject and a verb. They are called dependent because they depend on a main clause since they do not represent a complete thought, and thus cannot stand alone as a grammatically correct sentence.
