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Choose the best answer.(根据短文内容，选择最恰当的答案)
People usually check whether their keys, wallets and phones are with
them before going out. But many people in China now have one more important
thing to take, a face mask. They hope that it can protect them from the
polluted air.
Since January, many cities in China have seen a lot of hazy
days. During these days, people can only
see things that are very near them. In Beijing, only five days in January were
free of smog.
According to the Chinese Academy of Sciences, driving cars and burning
coal are two major factors for PM2.5, which is the main problem with air
pollution. Poor air is bad for people's health, especially for children and the
elderly. Air problems and environmental protection have become a concern for
the whole nation. Our government is taking action to prevent pollution and give
people a healthy living environment. It calls on people to make full use of
energy and resources and cut down on energy use.
