单项选择题

In the experiment we kept a watchful eye ______ the subtle changes and recorded every detail.

A．for
B．at
C．on
D．to
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单项选择题
The service operates 36 libraries throughout the country, while six ______ libraries specially serve the country side.
A．mobile
B．drifting
C．shifting
D．rotating
单项选择题
The newest satellite can ______ a thousand telephone conversations and a colour TV program at the same time.

A．carry
B．extend
C．bring
D．take
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