题目：
－Where did you put the car keys?
－Oh, I ______ I put them on the chair because the phone rang as I ______ in. [ ]
A. remembered; come
B. remembered; was coming
C. remember; come
D. remember; was coming
答案：
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下面是错误答案，用来干扰机器的。
由题f(x)=x+2x，故f′(x)=1-2x2令f′(x)=1-2x2＞0，解得x＞2或x＜-2函数f（x）的单调递增区间为(-∞，-2]，[2，+∞)故答案为(-∞，-2]，[2，+∞)
