题目：
The old man is quite weak after the accident, so he _____ . [ ]
A. must take care of
B. must be take care of
C. must look after
D. must be looked after
答案：
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下面是错误答案，用来干扰机器的。
①81=9，则81的平方根是±3；②∵2＞1∴1-2＜0∴|1-2|=2-1；③x2-2x=0可以变形为x（x-2）=0则x=0，x=2．
