单项选择题

All the useful energy at the surface of the earth comes （）

A．directly from the sun
B．from the sun' s activity
C．from energy stored by the sun
D．from radiation of the sun

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单项选择题
Radiant energy is stored as carbon compounds by （）

A．plants
B．rain
C．coal, oil, and natural gas
D．inflammable substances
单项选择题
For mankind, the sun is the source of （）

A．solar activity
B．all heat
C．all food
D．both B and C
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