More and more people have come to realize that if we had taken effective measures much earlier, the air quality ______ so seriously now.

A．is not polluted

B．would not be polluted

C．had not been polluted

D．would not have been polluted

子痰好发于：

A．老年

B．中、老年

C．中、青年

D．少儿

E．婴幼儿