At the first sight the planet Mars does not appear very welcome to any kind of life．It has very little oxygen and water,the temperature at night is below-50~Cand winds of 100 miles per hour cause severe dust storms．However,the surface of the planet seems to show that water flowed across it some time in the past,and it is believed that there is enough ice at the poles to cover the planet with water if it melts．Although there is no life on the Mars now,some scientists think that there may have been some form of life long time ago．At that time,the planet had active volcanoes;the atmosphere was thicker and warmer;and there was water．In fact,in some ways the Mars may have been similar to the Earth,where life exists.
Some people believe that the Mars could support life in the future if the right conditions were produced．The first step would be to warm the planet using certain gases which trap the Sun's heat in the planet's atmosphere．With warmth,water and carbon dioxide(二氧化碳),simple plants could begin to grow．These plants could slowly make the Mars more suitable for living．It is estimated that the whole process might take between 100,000 and 200,000 years．In the meantime,people could begin to live on the planet in special closed environments．They would provide a lot of useful information about conditions on the Mars and the problems connected with living there.
There could be life on the Mars in the future if
- A.it supported life in the past
- B.certain gases are used to cool the planet
- C.the atmosphere can be heated enough to grow simple plants
- D.the planet's volcanoes become as active as they were in the past
正确答案及解析
正确答案
解析
第二段大意是：如果要想改变火星的条件使之适合居住，首先要提高星球的温度，其方法是用某些气体收集太阳的热能。有了温度、水和二氧化碳，一些植物便可生长。慢慢地使星球适合生存。选项C，“人们可以以提高环境的温度的方式来使一些植物生长”是正确的。
