Many human activities over the last 200 years have been responsible (1) …………… polluting the air and damaging people’s health. Automobile engines and power plants burn combustible (2) …………… like gasoline and coal and allow toxic gases and smoke to

escape into the air. Some pollutants destroy the ozone layer, which is the thin blanket of gases that (3) …………… Earth from the Sun’s dangerous ultraviolet rays. Other pollutants contribute to (4) …………… warming by adding to the planet’s natural greenhouse effect. Still others create acid rain, a phenomenon that has disastrous (5) …………… on lake and forest habitats. Air pollution is not limited to industrial areas. Depending on the direction of the wind and its force, air pollutants may (6) …………… spread to other countries very far from

the source of the pollution.

     Big cities like Los Angeles and Mexico City are often covered by smog, a fog that occurs (7) ……………           air pollution. In 1952, the city of London, England, was enveloped by smog so thick that people on the streets had to feel their way around by (8) …………… the walls of buildings!

1.  a. for                       b. of                        c. to                      d. with

2.  a. chemicals                        b. means                 c. fuels                  d. matters

3.  a. covers                 b. protects               c. stops                 d. damages

4.  a. environmental     b. thermal               c. temperature       d. global

5.  a. affects                 b. causes                 c. sources              d. effects

6.  a. never                   b. even                    c. ever                   d. hardly

7.  a. because of                      b. in spite of           c. instead of          d. due of

8.  a. climbing              b. walking               c. touching                        d. putting up