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

He tried to avoid（）his friends in the street.

A．meets
B．met
C．meeting
D．to meet

单项选择题

You can't drink alcohol（）you are at least eighteen years old in some states of the US.

A．if
B．unless
C．though
D．when

相关试题