Let’s examine the sentence: “He was sent to the prison for his ______.” The sentence says that he was sent to jail and so we can assume that he committed something unlawful. As a legal action of imprisonment has taken place, a legal word is required by the sentence to specify the unlawful action. Such a legal word of unlawful action is “crime.” Other options, i.e. “sin,” “vice,” and “guilt,” are not legal words and do not denote an unlawful action. Hence, “crime” is the appropriate word required in the blank in the sentence. So, Option C is the correct answer.