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
By 1900 the American automobile age had begun--12 companies produced a ______ of more than 4,000 cars.
A．number
B．quantity
C．total
D．whole
单项选择题
His letter was so confusing that I could hardly make any ______ of it whatsoever.
A．meaning
B．sense
C．message
D．explanation
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