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
网友回答
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”。