问题

Scientists say it may be a few years ______ it is possible to test the new medicine onpatients.

A:because
B:after
C:since
D:before;

正确答案是：

同类题型

下列句中加横线的词语，与所给例句意义和用法相同的一项是 ( )例句：得复见将军于此

_____ is my sister.

Do you know whose shorts they are—–_I think they are ______. _______ shorts are red.

Your dream will come true _______ you put your heart and soul into it.

“Drive-ins” have large parking lots _____ customers are served in their cars by waitress.