It was in 1990 the medicine was tested on human patients.A. sinceB. thatC. beforeD. when

问题补充：

It was in 1990 the medicine was tested on human patients.

A. since

B. that

C. before

D. when

答案：

A. since

(答案→)B. that

C. before

D. when

解析：考查强调句型。强调句型的基本结构为It is/was被强调成分that/who其它成分；其最大的特点就是去掉it is/was…that/who…句子仍然成立。要注意强调句型能强调除谓语动词以为的所有的句子成分。本题中强调的是时间状语in 1990；句意：就是在1990年这种药物在人类的病人身上测试的。故B正确。