单项选择题

The ______ of human knowledge are being pushed further.

A．boundaries
B．borders
C．limits
D．edges
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单项选择题
The police have asked for the ______ of the public in tracking the whereabouts of the escaped criminals.
A．partnership
B．union
C．association
D．co-operation
单项选择题
Educational TV stations offer teaching in various ______ ranging from home nursing to art appreciation.
A．courses
B．directions
C．points
D．subjects
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