问题：
— Can you go swimming with us this afternoon?
— Sorry, I can"t. I ______ take care of my little sister at home because my mother is ill.
[ ]
A. can
B. may
C. must
D. would
— Can you go swimming with us this afternoon?
— Sorry, I can"t. I ______ take care of my little sister at home because my mother is ill.
B. may
C. must
D. would
— Sorry, I can"t. I ______ take care of my little sister at home because my mother is ill.
[ ]
A. can B. may
C. must
D. would
参考答案：