单项选择题

Questions 23 to 25 are based on the conversation you have just heard.

A．Why species don’t avoid extinction by adapting.
B．Why species become extinct at the rate they do.
C．Why humans aren’t extinct.
D．How many species aren’t extinct.
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单项选择题
A．Its chemical elements must be studied.B．Its temperature must be lowered.C．Big spaceships must be built.D．Its atmosphere must be changed.
A．Its chemical elements must be studied.
B．Its temperature must be lowered.
C．Big spaceships must be built.
D．Its atmosphere must be changed.
单项选择题
A．Nineteenth-century sea captains.B．The development of the steamship.C．The economic importance of sailing ships.D．Employment in the fishing and whaling industries.
A．Nineteenth-century sea captains.
B．The development of the steamship.
C．The economic importance of sailing ships.
D．Employment in the fishing and whaling industries.
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