填空题

American researchers say they have found that short-term increases in ozone lead to higher death rates in cities.
Ozone is a form of oxygen. The gas is produced naturally in the (26) atmosphere to protect the Earth against (27) from the sun. But human activity can also create ozone in the lower atmosphere.
Gasses from (28) and industry react with sunlight to form this ozone. Levels usually increase in the warmer months. Ozone is the main (29) in smog, the air pollution that is a (30) of fog and smoke.
Ozone has been linked to heart and lung problems especially, and to higher rates of hospital cases. Researchers from Yale University and Johns Hopkins University did the study. Michelle Bell of Yale was the lead (31) . The Journal of the American Medical Association published the results.
The research suggests that even a small increase in ozone, ten parts per thousand million, can lead to higher death rates the following week. The study found that the (32) daily number of deaths rose Point five percent. Heart and lung related deaths rose Point six percent. And deaths among older people rose Point seven percent.
The researchers controlled for other possible causes of death, such as hot weather or pollution from (33) matter. The study linked even a single day of increased ozone to more deaths the following week.
The study is one of the largest ever done of ozone and death rates. (34)
The United States Environmental Protection Agency is re-examining its air pollution rules. (35) . But the researchers say they found an increase in deaths even below the current levels.
(36) .