The function of the subordinate clause "that the mind contained unconscious thoughts and desires" is:
OB. It functions as a noun.
Explanation:
1. Nouns can act as subjects, objects, or complements in a sentence.
2. In this case, the subordinate clause "that the mind contained unconscious thoughts and desires" is functioning as the direct object of the verb "believed" in the sentence.
3. The clause serves as the object of the verb "believed" and answers the question "what" Freud believed.
4. Therefore, it acts as a noun by providing the information that is believed by Freud.