Air is very important to everything that lives. But the air we breathe is g小题1:___ dirty. People all over the world are looking for w小题2:___ to make it clean again.
Have you e小题3:__ watched the smoke from chimneys rising high in the air? Have you s小题4:__ the smoke from cars and trucks on roads or the smoke from planes? The smoke is not g小题5:___ to breathe. If we want to keep well and strong, we need to breathe c小题6:__ air.
W小题7:___ more and more factories everywhere and more and more cars, trucks and planes, it is getting harder and harder to do with the air p小题8:___.
Scientists have a小题9:__ found ways to stop or slow down some of the things that make the air dirty. They will not stop working u小题10:__ we have clean air again.