At the first sight the planet Mars does not appear very welcome to any kind of life. It ha
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.
Some scientists think there may have been life on the Mars in the past because ______.
A.there is no life there now
B.there is a large amount of water at the poles
C.the Mars may be able to support life in the future
D.conditions may have been similar to those on the Earth