a. Rhett was unwilling to listen to what his friend told him.
c. Whoever said that the early bird catches the worm was right.
In answer choice A, the noun clause is "what his friend told him". In this sentence the noun clause is the object of the preposition. A prepositional phrase always begins with a preposition, in this case - to, and ends with a noun or pronoun as the object of the preposition. Sometimes you can check by replacing the clause with a noun (Bob). Rhett was unwilling to listen to (Bob?). It works.
In answer choice C, the noun clause is "Whoever said that the early bird catches the worm". In this sentence the noun clause is the subject of the sentence. The subject of a sentence is always a noun or pronoun. It answers the question who or what is the sentence about. In this sentence the sentence is about "Whoever said that the early bird catches the worm".
