The old man served in the army in _________, when he was in _________．

A.1950’s … his twenties

B.1950’s … twenties

C.the 1950’s … his twenties

D.the 1950’s … the twenties

答案及解析： C

in the 1950’s或in the 1950s表示“二十世纪五十年代”，而in one’s twenties表示“在某人二十几岁的时候”。