How can you tell the difference between if a noun clause is a subject, direct object, or the object of preposition

They must function within another sentence pattern, always as nouns. A noun clause functions as a subject, subject complement, direct object, or object of a preposition. A noun clause usually begins with a relative pronoun like "that," "which," "who," "whoever," "whomever," "whose," "what," and "whatsoever."

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