单项选择题

Questions 19 to 22 are based on the conversation you have just heard.

A．The high temperatures required for its use.
B．The lack of trained environmental engineers.
C．The opposition of automobile manufacturers.
D．The high cost of materials used in its production.
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单项选择题
A．It influences the surface temperature of Mars.B．It protects living beings from harmful rays.C．It keeps a planet from overheating.D．It is the main component of the air people breathe.
A．It influences the surface temperature of Mars.
B．It protects living beings from harmful rays.
C．It keeps a planet from overheating.
D．It is the main component of the air people breathe.
单项选择题
A．Decide for himself what is best.B．Communicate his career hopes.C．Stop hindering his own progress.D．Look for another career.
A．Decide for himself what is best.
B．Communicate his career hopes.
C．Stop hindering his own progress.
D．Look for another career.
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