Read the passage and choose the best answer Air (23)…………..is caused of ill-health in human beings. In a lot of countries, there are laws limiting the amount of smoke which factories can (24)…………..although there is not enough information on the effects of smoke on the atmosphere. Doctors have proved that air pollution causes lung diseases. The gases from the exhausts of cars also (25)………….. air pollution in most cities. The lead in petrol produces a poisonous gas, which is often (26)…………..in busy streets circled by buildings. Children who live in areas where there is (27)…………..lead in the atmosphere cannot think as quickly as other children, and are clumsy when they use their hands. (23)...................