问题

How long do you think it will be _______ scientists succeed in providing a cure for cancer?

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

正确答案是：

同类题型

Traveling abroad is much than before.

My hair is long but isshort.

en the school was over, all thestudents scattered _____

Jane, why didn’t you go to Mary’s birthday party—Because ________________________

Mr Li ____ England. He ____ London for two weeks.