Air pollution is a cause of ill-health in human beings. In a lot of countries there are laws limiting the amount of smoke (13) _______ factories can produce. Although there isn’t enough information on the effects of smoke in the atmosphere, doctors have proved that air pollution (14) ______ lung diseases. The gases from the exhausts of cars have also increased air pollution in most cities. The lead in petrol produces a (15)___________ gas which often collects in busy streets surrounded (16)___________ high buildings. Children who live in areas where there is a lot of lead in the atmosphere cannot think as quickly as other children and are clumsy (17)____________ they use their hands. There are other long-term effects of pollution. If the gases in the atmosphere continue to increase, the earth’s (18)__________ may become warmer. A lot of the ice near the Poles may melt and may cause serious floods. 13. A. who B. whom C. which D. whose 14. A. gives B. makes C. causes D. cures 15. A. inedible B. generous C. terrific D. poisonous 16. A. by B. in C. inside D. on 17. A. because B. when C. if D. though 18. A. weather B. environment C. atmosphere D. climate