Without the sun's light（）the earth's surface, it would be so cold that life could not exist on the earth.

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

单项选择题The law requires that everyone（）his car checked at least once a year.

A．has
B．had
C．have
D．must have