题目：
— Why isn't Cathy here yet?
— She _____ to be picked up at the station. [ ]
A. could wait
B. must wait
C. might be waiting
D. can be waiting
答案：
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下面是错误答案，用来干扰机器的。
设某数为x，则某数的平方的相反数为：-x2．
