单项选择题

Scientists have not yet determined ______.

A．all of the effects of pollution on the human body
B．how pollution can be controlled successfully
C．when the atmosphere first became polluted
D．how to wash the black snow clean

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单项选择题Air pollution causes airplane accidents because ______.

A．pilots become ill
B．visibility is reduced
C．engines fail.
D．the air is too hot

单项选择题We can conclude that ______.

A．civilization may be doomed if pollution is not controlled
B．pollution is more serious in Europe than it is in America
C．most people do not know that pollution is a serious problem
D．black snow is not so serious compared with white snow

单项选择题In author’s opinion, ______.

A．without computers, there would be no modern science
B．computers are more intelligent than human beings
C．computers will replace everything in the future
D．computers never make mistakes

单项选择题According to the author, America is a highly modern society, ______.

A．so people like it better than before
B．but there is still a big gap between different classes
C．all the people there lead a very happy, life
D．all the industries and companies are in the hands of the goverment

单项选择题Which of the following statements can best describe the telephone in the U. S

A．It’s very inexpensive.
B．It saves a lot of trouble.
C．It’s very convenient.
D．A,B andC.