People need to breathe. If they don't breathe, they (1)............ die.

People need to breathe. If they don't breathe, they (1)............ die. But how to clean is the air people breathe? If they breath (2)............ air, they will have breathe problems and become (3)........ Plants and animals need (4)............... air, too. A lot of things in our lives create harmful gases and (5)............. the air dirty like cars, motorbikes and factories. Dirty air is called polluted air.