Correct answer: What commercials promise is not always what consumers can depend upon.
Explanation: The noun clause of the sentence above is "What commercials promise". A noun clause is a dependent clause that acts as a noun, and it cannot stand alone in a sentence. Noun clauses begin with words such as what, how, that, when, whatever, where, whichever, who, whether, which, whoever, whom, whomever, and why.
