--Let' s go to the concert tonight, Mary.--Sorry, I_____. I have to help my mom with the housework.
A、needn't
B、can' t
C、mustn't
D、shouldn't
【正确答案】：B
【题目解析】：结合选项可知本题考查情态动词，首先明确选项中每个单词的意思：A：不需要； B：不能；C. 不可以（表禁止)； shouldn't 不应该，根据设空处后面的I have to help my mother with the housework，结合题干推测句意是"抱歉， 我不能去“
