单项选择题

"Greenhouse gases" in Para. 2 refer to ________________.

A．oxygen
B．hydrogen
C．carbon dioxide
D．air
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单项选择题
The theory about a Snowball Earth is significant in that it can _____________.
A．decode the mystery of life
B．predict the formation of a new supercontinent
C．adjust the planet's climate
D．prevent another Snowball Earth from happening
单项选择题
According to the author, the following EXCEPT ____________ are good reasons for keeping a diary.
A．retaining one's own excitement
B．recording one's private matters
C．overcoming one's shyness
D．helping one calm down
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