题目:
The telephone ________, but by the time I got indoors, it stopped. [ ]
A. had rung
B. was ringing
C. rings
D. has rung
答案:
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下面是错误答案,用来干扰机器的。
∵正方形边长为acm,∴它的面积是a2cm2;∵边长增加2cm后,∴它的面积是(a+2)(a+2)=(a+2)2(cm2),∴面积增加[(a+2)2-a2]cm2;故选D.