单项选择题

（） much is known about what occurs during sleep, the precise function of sleep and its different stages remains largely in the realm of assumption.

A．Because
B．For
C．Since
D．While

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单项选择题
（） the help of their group, we would not have succeeded in the investigation.

A．Besides
B．Regardless of
C．But for
D．Despite
单项选择题
All human beings have a comfortable zone regulating the （） they keep from someone they talk with.

A．distance
B．scope
C．range
D．boundary
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