单选题 American researchers say they have found the strongest connection between ozone(臭氧) pollution and damage to health. Their findings show that short-term increases in ozone lead to higher death rates in cities.
Ozone is form of oxygen. The gas is produced naturally in the upper atmosphere to protect the earth against radiation from the sun. But human activities can also create ozone in the lower atmosphere. Gasses from cars and industry react with sunlight to form this ozone. Levels usually increase in the warmer months. Ozone is the main chemical in smog, the air pollution that is a combination of fog and smoke.
Ozone has been connected with heart and lung problems especially, and with higher rates of hospital cases. Researchers from Yale University and Johns Hopkins University did the study. Michelle Bell of Yale was the lead researcher. The Journal of the American Medical Association published the results. The researchers collected information on 95 American cities. These contain about 40 percent of the national population. The study compared death rates to ozone levels between 1987 and 2000. The research suggests that even a small increase in ozone, 10 parts per thousand million, can lead to higher death rates the following week. The study found that the average daily number of deaths rose point-six percent. And deaths among older people rose point-seven percent.
The study is one of the largest ever done of ozone and death rates. The researchers note that ozone is widespread in the United States and many other countries. The United States Environmental Protection Agency is re-examining its air pollution rules. The limit at present for ozone is 80 parts per thousand million for an eight-hour period. Limits were higher in the past. But the researchers say they found an increase in deaths even below the present levels.

单选题 The passage mainly tells us ______.

A、 death rates are connected with ozone levels
B、 ozone is made up of two parts
C、 lung cancers are connected with ozone levels
D、 the environment goes worse and worse in American

【正确答案】 A

【答案解析】[解析] 文章第一段第一句话揭示文章的主要内容，文章主要说的是死亡率和臭氧水平的关系。可知A为正确答案。

单选题 The underlined word "smog" (in Paragraph 2) mean"______ ".

A、 a kind of brown smoke
B、 the main chemical in ozone
C、 smoke caused by air pollution
D、 brown unhealthy air caused by smoke from cars or factories and fog

【正确答案】 D

【答案解析】[解析] 第二段最后一句话the air pollution that is a combination of fog and smoke是对smog的解释。可知D为正确答案。

单选题 According to the results of the study from Yale University and Johns Hopkins University, we
know that ______.

A、 95 American cities contain 40% of the national population
B、 children are easy to suffer from an increase in ozone
C、 a small increase in ozone can cause higher death rates
D、 the study placed the time between 1987 and 2000

【正确答案】 C

【答案解析】本题属细节题，从第三段的句子“The research suggests that even a small increase in ozone，10 parts per thousand million，can lead to higher death rates the following week”可知C选项正确。

单选题 According to the passage, we can infer that ______.

A、 the present ozone level in America is safe to people
B、 there is no direct connection between ozone and death rates
C、 the study of ozone and death rates has been done several times
D、 America has a worse problem with ozone than other countries

【正确答案】 C

【答案解析】[解析] 从第四段的第一句话“The study is one of the largest ever done of ozone and death rates”可以看出，关于臭氧和死亡率关系的研究已经进行过好多次。可知C选项正确。

单选题 Which is not true according to the passage? ______.

A、 American researchers' findings show that short-term increases in ozone lead to higher death rates in cities.
B、 Ozone is not a form of oxygen.
C、 Ozone has been connected with heart and lung problems.
D、 Researchers say they found an increase in deaths even below the present levels.

【正确答案】 B

【答案解析】[解析] 从第二段的第一句话可以判断B是错误的。