Choose the correct answer A, B, C or D to complete the passage. 

People need to breathe. If they don’t breathe, they (1) ____________ die. But how clean is the air people breathe? If they breathe (2) ___________ air, they will have breathing problems. Plants and animals need (3) __________ air too. A lot of the things in our lives create harmful gases and(4) _________the air dirty, like cars, motorbikes, and factories. Dirty air is called polluted air. Air pollution can also make our Earth warmer.