单项选择题

The oldest kind of computer, the abacus, has been used since ______.

A．600
B．700
C．800
D．500
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单项选择题
The computer will soon affect ______.
A．people in large cities
B．people in developed countries
C．all humanity
D．the Western world
单项选择题
The computations of the computer are measured in ______.
A．seconds
B．microseconds
C．milliseconds
D．nanoseconds
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