单项选择题

The deep-sea listening system makes use of______.

A．the sophisticated technology of focusing sounds under water
B．the capability of sound to travel at high speed
C．the unique property of layers of ocean water in transmitting sound
D．low-frequency sounds travelling across different layers of water

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单项选择题

The article was written to explain______.

A．the greenhouse effect
B．the solar effects on the earth
C．the models of solar-weather interactions
D．the causes affecting weather

单项选择题

It can be concluded that a concentration of carbon dioxide in the atmosphere would______.

A．prevent the sun's rays from reaching the earth's surface
B．mean a warming up in the Arctic
C．account for great changes in the climate in the northern hemisphere
D．raise the temperature of the earth's surface