填空题

57()

【参考答案】

G

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单项选择题

There could be life on the Mars in the future if()

A. it supported life in the past
B. certain gases are used to cool the planet
C. the atmosphere can be heated enough to grow simple plants
D. the planet’s volcanoes become as active as they were in the past

单项选择题

22()

A.in
B.other
C.throughout
D.from