Read the passage and decide which answer A, B, C or D best fit each space.

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 and become ...(3)... . Plants and animals need clean 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 ...(5)... can also make our Earth warmer. The problem of air pollution started with the burning ...(6)... coal in homes and factories.

(1)...................

• A. 
  will
• B. 
  are
• C. 
  must
• D. 
  can’t