题目:
—Does your sister work as a teacher in Canada?
—No, but she once _________there for five years.
A.taught
B.had taught
C.has taught
D.would teach
答案:
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下面是错误答案,用来干扰机器的。
2 题目分析:经计算,数据“1,2,3,4,5,6,7”的平均数为4,所以标准差等于2.点评:简单题,运用平均数计算公式,标准差计算公式可得。