Air (20) ________ is caused of ill-health in human beings. In a lot of countries, there are laws limiting the amount of smoke which factories can (21) ________ 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 (22) ________ air pollution in most cities. The lead in petrol produces a poisonous gas, which is often (23 ________ in busy streets circled by 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. 20. A. pollute B. pollution C. polluted D. polluting 21. A. to produce B. produced C. producing D. produce 22. A. increased B. increasing C. to increase D. increase 23. A. collected B. collect C. collecting D. collects VOTE 5 SAO +CTLHN NHƯNG GIẢI THÍCH Ạ