It was not rare(稀少) in that people in fifties were going to school for further study.A. 90

问题补充：

It was not rare(稀少) in that people in fifties were going to school for further study.

A. 90s; the

B. the 90s; /

C. 90s; their

D. the 90s; their

答案：

A. 90s; the

B. the 90s; /

C. 90s; their

(答案→)D. the 90s; their

解析：考查词组：第一空考查in the+年代的复数或加’s,是在多少世纪多少年代，第二空考查in one’s 数词的复数，表示“在某人多少岁的时候”，句意：在90年代，很少有人在50几岁的时候还去上学深造的。选D。