单项选择题

Once environmental damage(), it takes many years for the system to recover.

A. had done
B. is done
C. is to do
D. does

<上一题目录下一题>

热门试题

单项选择题

()is known to the world, Mark Twain is a great American writer.

A. As
B. That
C. Who
D. Which

单项选择题

I like climbing mountains() my brother prefers water sports.

A. as
B. while
C. when
D. for

相关试题