My father served in the army in when he was in .
A. 1950’s; twenties
B. the 1950s; his twenties
C. 1950’s; the twenties
D. 1950s; the twenties
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A. 1950’s; twenties
(答案→)B. the 1950s; his twenties
C. 1950’s; the twenties
D. 1950s; the twenties
解析：考查数词。In the 1950s/1950’s在20世纪50年代；in one’s twenties在某人20多岁时。句意：我父亲参军是在20世纪50年代，那时他20多岁。