Air pollution is a (1) _______ of ill-health in human beings. In a lot of countries, there are laws limiting the amount of smoke which factories can produce. (2) _______ there isn’t enough information on the effects (3) _______ smoke in the atmosphere, doctors have proved that air pollution causes lung diseases.

The gases from the exhausts of cars have also (4) _______ air pollution in most cities. The lead in petrol produces a poisonous gas (5) _______ often collects in busy streets surrounded by 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 when they use their hands.