As people in Beijing and northern China struggle with severe air pollution this winter,the toxic(有毒的)air is also making life hard for plants and even food crops of China．
"in the last 50 years there has been a 1 6-fold increase in ozone(臭氧)pollution”in the Beijing area，said Hanqin Tian of Auburn University in Alabama,who studies the effects of China's pollution and climate change on plants．
Ozone is particularly harmful to plants because it damages the pores(气孔)  on leaves，called stomata,which plants use to regulate how much water evaporates from the leaves．That，in turn，affectS how much water a plant must take up through its roots．Changes in water uptake by plants have been documented in other parts of the world，including the United States，as having major impacts on regional groundwater and surface water supplies．
In studies of the long-term productivity of plants，Hanqin Tian and some of his colleagues show that ozone pollution,along with climate change，has been lowering plant productivity in China,which reduces the amount of carbon and other pollutants that the plants Can absorb to fight all the emissions from the burning offossil fuels．
The worst effects on plants are likely to be in areas where the growing pollution problem is just fairly new, said Arthur Chappelka, also a plant researcher at Auburn University．Some plants are more resistant to pollutants than others，he said，and the plants that are living today in long-polluted urban areas are likely to be only those that are very pollution tolerant．
Away from the cities, however, where crops are necded to feed China’s yast population, the effeets of the growing pollution on crops is a significant concern.
“In some ways it affects the crop production and food securiy of China,”said Hanqin Tian.“Air quality is really important for human health, plants and ecosystem and sustainability.”
The problem is bound to get worse as China continues to develop economically, he said, and so he and other researchers continue to urge the Chinese government to take action to reduce emissions from cars and industries.
ozone does harm to plants mainly by ________.

A．exposing them to strong sunlight

B．damaging the structure of their leaves

C．adding more pores to the roots

D．making the land unfit for the plants to grow

Which of the following statement does Hanqin Tian support?

A．Ozone pollution has increased 1 6 times in the past 30 years．

B．Ozone pollution has lowered plant productivity alone．

C．Plants can take in a large amount of carbon and other pollutants．

D．The toxic air has few effects on food supply in China．

What Can we infer from the passage?   

A．Healthy foods are not available in Beijing．

B．Some kinds of plants aren’t affected by air pollution．

C．Crops in China are hard to feed its large population．

D．People should stop developing economically

According to the passage，the Chinese govemment should

A．care more about developing economy

B．reduce the number of cars and industries

C．continue to make more researches

D．take measures to reduce carbon emissions

What′S the best title of the passage?

A．Polluted air damages plants and crops

B．Air pollution is becoming more serious

C．China’s air pollution and climate changes

D．Food security in China