Fill in each gap a suitable word from the box. Air pollution is caused of ill health in human beings. In a lot of countries, there (1)______ laws limiting the amount of smoke which factories can produce. Doctors have proved that air pollution causes lung diseases. The gases from the (2) ______ of cars have also increased air pollution in most cities. The lead in petrol produces a poisonous gas, which is often collected in busy streets circled by high (3) ______. Children who (4) ______ in areas where there is a lot of lead in the atmosphere can not think as quickly as other children, and are clumsy when they use their hands. 1. A. are                                  B. is                              C. were                                   D. have 2. A. exhausts                         B. exhausted                C. exhausting                         D. exhaust                   3. A. building                          B. buildings                  C. cities                                  D. house          4. A. live                                 B. living                       C. has lived                            D. lived