1.   A federal law spells out the penalties for missing the deadline to cut air pollution.

2.   A report published by the government has revealed the extent of air pollution in the area.

3.   A scientist does experi merits, and no experiment I have ever done proves that air pollution is hurting those trees.

4.   Air pollution can cause breathing problems for some people.

5.   Air pollution has become one of the most significant health problems of our time.

6.   Air pollution is our most serious environmental problem.

7.   Air pollution is particularly bad in urban areas.

8.   By last year the crisis had reached such proportions that Southern California introduced radical new regulations to control air pollution.

9.   Cars and industry in El Paso contribute to the air pollution, of course.