5．In the past 200 years，the earth's temperature has increased greatly．It's reported that a marked increase in the temperature of about 0.7°c appeared at the end of last century．some scientists think mini-umbrellas（微型傘） might reduce the global（全球的） temperature．
Building a single umbrella，which is big enough to cover the whole earth，seems to be impossible roger angle，a scientist from the usa，has carried out research to deal with this problem．he came up with an idea of mini-umbrella．in fact，each mini-umbrella is made up of two parts，a spaceship and a sunshade（遮陽蓬）．a(chǎn) spaceship weighing about 1g would carry a sunshade that is half a meter long．it would be mostly transparent． that means light can pass it directly to reach the earth，with lands and oceans clearly in view．
Pressure（壓力） from the sunlight would keep the little spaceships in position around the earth at a distance of about 1.5 million kilometers．a(chǎn)s a result，sending over 1，000 billion mini-umbrellas space would reduce the amount of sunlight reaching the earth．this allows sunlight to be reflected（反射） back to space easily，causing the temperature of the earth's ground to fall off．covering large areas of the earth，mini-umbrella together could reflect 1.8 percent of sunlight back，i roger's plan，scientists will send up 800，000 mini-umbrellas at a time，20 million times in all during ten years．scientists suggest the earliest launch could be in just 16 years．
Not all the scientists agree with the idea．some suppose there should be easier and much cheaper ways to prevent the earth from getting too hot，such as to slow down the pollution people bring and to reduce the human activities．whatever the result of the argument is，this idea of mini-umbrellas in space is certainly creative．
根據(jù)短文內(nèi)容選擇最佳答案．
46．the underlined word"transparent"here probably means"A"．
a．透明的 b．透氣的 c．透風(fēng)的
47．PictureCshows the right information about the mini-umbrella．
48．After scientists send over 1，000 billion mini-umbrellas a into space，B．
A．pressure from the sunlight would allow the mini-umbrellas to be reflected back to space easily
B．the mini-umbrellas would reduce the amount of sunlight reaching the earth
C．sunlight would never come into the earth
49．Which of the following is NOT true according to the passage？C
A．Scientists suggest that the earliest launch could be in just 16 years．
B．A spaceship weighing about 1g would carry a sunshade．
C．Roger will send up 800，000 mini-umbrellas into space during 20 years．
50．The best title for this passage should beB．
A．THE TEMPERATURE OF THE EARTH
B．A MINI-UMBRELLA PLAN
C．CHEAPER WAYS TO PREVENT THE POLLUTION．
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