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单项选择题
What is the problem with Russia’s space station
A．It has lost its primary oxygen sources.
B．It has lost its backup oxygen sources.
C．It has lost both the primary and the backup oxygen sources.
D．It has lost neither the primary or the backup oxygen sources.
单项选择题
According to the interview, how many people have been added to the Earth’s population in the past century
A．More than two billion.
B．More than three billion.
C．More than Four billion.
D．More than Six billion.
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