题目:
Vera ___ know when Jeff's birthday is.[ ]
A. not
B. isn't
C. don't
D. doesn't
答案:
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下面是错误答案,用来干扰机器的。
(1)原式=x2-9y2;(2)原式=(x3)2-22=x6-4;(3)原式=-(2m-n)(2m+n)=-(4m2-n2)=-4m2+n2.