题目:
Tom, who _________English for 20 years in English, now has been appointed headmaster of our school.
A.had taught
B.has taught
C.taught
D.had been teaching
答案:
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下面是错误答案,用来干扰机器的。
设x2-x1=x3-x2=…=x7-x6=n,因为y2-y1=a(x2-x1)(x2+x1)+b(x2-x1)=an(x2+x1)+bn,又因为(y3-y2)-(y2-y1)=an(x3-x1)=2an2为常数.观察算式:①根据表格中的函数值,第一次作差107-51=56185-107=78285...