单项选择题

What is one of the things that must be done before man can live on Mars（）

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.

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单项选择题
According to the speaker, what would good negotiators do（）

A．Study the case carefully beforehand.
B．Stick to a set target.
C．Appear friendly to the other party.
D．Try to be flexible about their terms.
填空题
S5（）
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