单项选择题

Why blue lights are installed in many train stations()

A. Because they do not hurt human eyes.
B. Because they are cheaper than regular ones.
C. Because they can help people at night.
D. Because they can reduce the number of suicides.

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单项选择题

In the Bay Area, a family needs to earn()the amount they do in other areas.

A. twice
B. five times
C. four times
D. three times

单项选择题

Some scientists think there may have been life on the Mars in the past because ()

A. there is no life there now
B. there is a large amount of water at the poles
C. the Mars may be able to support life in the future
D. conditions may have been similar to those on the Earth