I wonder who cleaned the house yesterday.It______have been John

I wonder who cleaned the house yesterday.It______have been John because he and I were out of town all day.
A、mustn’t
B、needn’t
C、couldn’t
D、won’t
【正确答案】：C
【题目解析】：此题考察的是情态动词的用法。情态动词可以用于表推测，肯定句中用must, 否定的推测用can’t/couldn’t。此句的意思是我好奇谁昨天打扫了屋子。不可能是John因为我和他昨天整天都出城了。