单项选择题

What do we learn about deserts from this text

A．Deserts can change into green and fertile areas.
B．Certain areas have always been desert.
C．Deserts were once the home of elephants and giraffes.
D．Deserts have been growing since the beginning of the world.

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热门试题

单项选择题

Which of the following is NOT mentioned as a possible cause of lung diseases

A．The burning of coal
B．Long-term exposure to smog
C．Exposure to nitrogen dioxide
D．Attending school camps

单项选择题

The relationship between exposure to ______ has not yet been determined.

A．ozone and fall in lung function
B．ozone and lung diseases such as asthma
C．nitrogen dioxide and worse lung function
D．smog and chronic bronchitis and emphysema