Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct word for each of the blanks.

Air  pollution  occurs  when  wastes  dirty  the  air.  People  produce  most  of  the  (44)  ______  that  cause  air pollution.  Such  wastes  can  be  in  the  form  of  gases  or  particles  of  solid  or  liquid  matter.  These  substances result chiefly from burning (45) _______ to power motor vehicles and to heat buildings. Industrial processes and the (46) _______ of garbage also contribute to air pollution. Natural pollutants (impurities) include dust, pollen, soil particles, and naturally occurring gases.

     The  rapid  growth  of  population  and  industry  and  the  increasing  use  of  automobiles  and  airplanes  have made air pollution a (47) _______ problem. The air we breathe has become so filled with pollutants that it can cause (48) _______ problems. Polluted air also harms plants, animals, building materials, and fabrics. In addition, it causes damage by altering the earth’s atmosphere.

Điền ô số 48

A. pollution

B. health

C. preserving

D. dirty