Mr. Bill Clinton was elected President of the United States in 1990s.A. the; the B. a;

问题补充：

Mr. Bill Clinton was elected President of the United States in 1990s.

A. the; the

B. a; the

C. the; 不填

D. 不填; the

答案：

A. the; the

B. a; the

C. the; 不填

(答案→)D. 不填; the

解析：句子所要表的意思是在九十年代，比尔.克林顿被选为美国总统。本句中只是要说克林顿被选为总统这件事，究竟是哪国总统，哪一届总统并不重要，总统只是一种职业的代称，故此处不用冠词。时间状语则为固定结构，in +the +年份复数，因为是特指在某个年代，故前面需加定冠词the。故选D