问题：
David can"t go to take part in the sports meeting, because he"ll ________ take care of his mother
who is ill.
[ ]
A. must
B. has to
C. have to
D. needs to
David can"t go to take part in the sports meeting, because he"ll ________ take care of his mother
who is ill.
B. has to
C. have to
D. needs to
who is ill.
[ ]
A. must B. has to
C. have to
D. needs to
参考答案：