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  3. At the first sight the planet Mars(火星)does not appear very welcome to any kind of life. It has very little oxygen and water, the

At the first sight the planet Mars(火星)does not appear very welcome to any kind of life. It has very little oxygen and water, the

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问题     At the first sight the planet Mars(火星)does not appear very welcome to any kind of life. It has very little oxygen and water, the temperature at night is below -50°C and 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, 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______.
选项 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
答案D
解析 事实细节题。第一段的后三句说明了“尽管火星上以前没有生命，但那时候火星上有活跃的火山、稠密暖和的空气，还有水”，这些都是“也许火星上过去有生命形式的存在”的条件。所以由此推断火星上之前有生命存在。
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