Air is very important to everything that lives. But the air we breathe is g___ dirty. People all over the world are looking for w___ to make it clean again.
Have you e__ watched the smoke from chimneys rising high in the air? Have you s__ the smoke from cars and trucks on roads or the smoke from planes? The smoke is not g___ to breathe. If we want to keep well and strong, we need to breathe c__ air.
W___ 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___.
Scientists have a__ found ways to stop or slow down some of the things that make the air dirty. They will not stop working u__ we have clean air again.