Question

My father served in the army in ____when he was in____

A.1950;twenties
B.the 1950's;his twenties
C.the 1950's;the twenties
C.1950's;the twenties

Answer 1

答案是选B，第一个空填的是the 1950's， in the 1950's 意思是在20世纪50年代，the不能省略；
而第二个空填的是his twenties， 来自于短语 in one's ( twenties, thirties, forties……）意为：在某人…十岁时。因此，in his twenties意思是：在他20岁时。

Answer 2

B in one's＋数字的复数形式　　在某人几（十）岁的时候

Answer 3

c