单项选择题

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

A．has done
B．is to do
C．does
D．is done
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单项选择题
Was it is 1969 ______ the American astronaut succeeded ______ landing on the moon
A．when, on
B．that, on
C．where, in
D．that, in
单项选择题
Mike's father as well as his mother insisted that he ______ home.
A．stayed
B．could stay
C．has stayed
D．stay
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