You nailed it if you chose C! "Ineffable" is used when something is so deeply felt that you cannot use words to describe it. In this case, only Answer C makes it clear that the man in the example sentence is so happy that he can't find any words to express it. "Ineffable" comes ultimately from the Latin prefix "-in," meaning "not," and the verb "effari," which means "to speak out." "Ineffable" can be used of good feelings ("his ineffable joy") or bad ones ("her ineffable and complete disgust").