51. c
52. b
53. c
54. a
55. b
56. c
57. b
58. d
59. a
60. c

Air pollution is a cause of ill-health in human beings. In a lot of countries there are laws limiting the amount of smoke which factories can produce. Although there isn't enough information on the effects of smoke in the atmosphere, doctors have proved that air pollution causes lung diseases.
The gases from the exhausts of cars have also increased air pollution in most cities. The lead in pertrol produces a poisonous gas which often collects in busy streets surrounded by high buildings. Children who live in areas where there is a lot of lead in the atmosphere can't think as quickly as other children and are clumsy when they use their hands.
There are other long-tern effects of pollution. If the gases in the atmosphere continue to increase, the Earth's climate may become warmer. A lot of the ice near the Polesma melt and may cause serious floods.