He finished middle school.A. in twenty in 1950sB. at twenty in the 1950sC. in twenties in

问题补充：

He finished middle school.

A. in twenty in 1950s

B. at twenty in the 1950s

C. in twenties in the 1950s

D. at twenties in the 1950s

答案：

A. in twenty in 1950s

(答案→)B. at twenty in the 1950s

C. in twenties in the 1950s

D. at twenties in the 1950s

解析：本题干语意为：他在二十世纪五十年代当他二十岁时就中学毕业了。at twenty表“二十岁”=at the age of twenty;in the 1950s表“二十世纪五十年代”。