All the useful energy at the surface of the earth comes from the activity of the sun. The sun heats and feeds mankind. Each year it provides men with two hundred million tons of grain, and nearly ten million tons of wood.
Coal, oil, natural gas, and all others fuels are store-up(储藏)energy from the sun. Some was collected by this season's plants as carbon compounds. Some was stored by plants and trees ages ago.
Even waterpower comes from the sun. Water turned into vapor by the sun falls as rain. It runs down the mountains and is turned into electric power.
Light transmits(传输)only the energy that comes from the sun's outer layers, and much of this energy never arrives on earth. About nineteenths of it is absorbed by the atmosphere of the earth. In fact, the earth itself gets only one half-billionth of the sun's entire output of radiant(辐射)energy.
6.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
7.For mankind, the sun is the source of ______. [ ]
A.activity B.all heat
C.all food D.both B and C
8.The sun's energy indirectly provides the earth with ______. [ ]
C.light D.both A and B
9.The largest part of the energy from the sun is ______. [ ]
A.stored by the season's plants
B.turned into fuel
C.absorbed by the earth's atmosphere
D.used for electric power
10.Of the sun's entire output of radiant energy, the earth receives ______. [ ]
A.nearly all B.about half
C.a very small part
D.all that come from the sun's outer layers