单项选择题

What causes great intensity of radio signals

A．The x-rays and atomic particles.
B．The thermal activity in core.
C．The ultra-violet rays.
D．Other gases on the surface of the sun.
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单项选择题
Why does the photosphere shine so brightly and send out x-rays and ultra-violet light
A．Because atoms are being broken down and built up in the central parts of the sun.
B．Because the photosphere send out light.
C．Because dark spots are much darker than the photosphere.
D．None of the above.
单项选择题
Why should we care about the extinction of wildlife
A．We need more predators.
B．We are required to by the government.
C．Natural imbalance will threaten human"s life.
D．None of the above.
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