Read the following passage and circle the letter A, B, C, or D to indicate the correct word or phrase that best fits each of the numbers blanks.
People need to breathe. If they don’t breathe, they ___(1)___ die. But how clean is the air people breathe? If they breathe dirty air, they will have breathing problems and become ___(2)___. Plants and animals need clean air too. A lot of the things in our lives create harmful gases and ___(3)___ the air dirty, like cars, motorbikes and factories. Dirty air is called ___(4)___ air’. Air pollution can also make our Earth warmer . The problem of air pollution started with the burning of coal in homes ___(5)___ factories.