Children in southern California may be breathing easier these days compared with the 1990s, thanks to a big reduction in air pollution, a new study suggests.

Researchers found that as air quality improved in five Los Angeles-area communities over two decades, so did children's lung development.

Experts said the findings, published in the March 5 issue of the New England Journal of Medicine, suggest a major public health benefit from cleaner air: Kids' lung function not only matters in the short-term, but is also tied to their risk of developing heart and lung disease later in life. The results are welcome news, said study leader W. James Gauderman, a professor of preventive medicine at the University of Southern California, Los Angeles.

The findings are based on three different groups of children who had their lung function tested repeatedly between the ages of 11 and 15 -- a critical period for lung development. All were from the same five communities near Los Angeles, but were tested at different time periods: 1994-1998, 1997-2001, or 2007-2011.

"One of our most important findings," Gauderman said, "was that the percentage of children with abnormally low lung function at age 15 declined from nearly 8 percent, to less than 4 percent in the most recent group."

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1.In which part of America has the air quality improved a lot?

A In northern California.

B In southern California.

C In South Carolina.

D In North Carolina.

解析：选B。B 细节理解题。根据文章第1段Children in southern California…可知，故选B。

2.Children’s_______develop as air quality improved.

A eyesight.

B lung function.

C hearing.

D smelling.

解析：选B。B 细节理解题。根据第2段as air quality improved … so did children's lung development.可知，故选B。

3.When is the critical period for lung development?

A 11-15.

B 11-16.

C 5-11.

D 9-15.

解析：选A。A 细节理解题。根据第4段第1句…ages of 11 and 15 -- a critical period for lung development.可知，故选A。

4.The word “critical” in “a critical period” probably means________.

A urgent

B very important

C disapproving

D dangerous

解析：选B。B 语义推测题。critical此处意为“重要的，关键的”，ACD选项分别为危急的、批评的、危险的，均不符合句意，故选B。

5.Which statement is RIGHT according to the passage?

A Air pollution was once a big problem in southern California.

B More and more cars cause bad air pollution in California.

C Air pollution once caused a large number of death in California.

D There in no need to worry about the air pollution now in California.

解析：选A。A 内容理解题。文中并未提到汽车的增加是加州空气质量变差的原因；也未提到空气污染导致大批人员死亡；至于现在无需担心加州空气污染本身就是错误选项，故选A。