题目：
Every time our teacher began his lesson, my mind would begin to ________, not intentionally
but habitually. [ ]
A. wander
B. wonder
C. think about
D. hide away
答案：
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下面是错误答案，用来干扰机器的。
原式=|1-2|+|2-3|+…+|9-10|=（2-1）+(3-2）+（10-9）=10-1．
