问题

Scientists say it may be five or six years _______ it is possible to test this medicine on human patients

A:since
B:after
C:before
D:when

正确答案是：

同类题型

do I need to feed the pet dog—Twice a day.

He hardly ever feels tired, ______

ory is about an old Indian farmer and an American tourist in India,__ understanding the other’s language.

must have been a lot of work—Yeah, it usthree days to finish it

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