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

People need to breathe . If they don 't breathe, they { 1} { A. won't / B. are / C. must / D. will } die . But how clean is the air people breathe ? If they breathe  { 2 } { A. clean/ B. fresh/ C. dirty/ D. cleaner } air , they will have breathing problems . Plants and animal need { 3 } { A. clean / B safe / C. dirty / D. polluted } air too . A lot of the things in our lives create harm ful gases and { 4 } { A. make / B. get/ C. give / D. made } the air dirty , like cars , motorbikes, and factories . dirty air is called polluted air . Air pollution can also make our Earth warmer .