单项选择题

Although we are not sure why we sleep, there is no doubt ______ we need to do so.

A．whether
B．why
C．what
D．that
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单项选择题
The ______ of medical knowledge are being pushed farther outwards as time goes on.
A．edges
B．borders
C．boundaries
D．frontiers
单项选择题
The police suspected that the sectary might be ______ of the murder.
A．guilty
B．conscious
C．careful
D．impatient
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