The old man served in the army in _________, when he was in _________．
A.1950’s … his twentiesB.1950’s … twentiesC.the 1950’s … his twentiesD.the 1950’s … the twenties在线课程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”。