问题

Not until all the fish died in the river _____ how serious the problem of water pollution was. [ ]

A: did they realize
B: they did realize
C: had they realized
D: they had realized

正确答案是：

同类题型

I will go to New York City next week. I can’t wait it!—__________________.

. It’s true that he did write someexcellent poems, but he is ______ known as a playwright.

Grace kept on __________ , although she was ill.

_______, a learned man makes fewer mistakes in life than a man without knowledge

_______ animals are dying and there will be ______space for them.