单选题 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℃ 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.

单选题 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
【正确答案】 D
【答案解析】[解析] 事实细节题。第一段最后一句“In fact, in some ways the Mars may have been similar to the Earth, where life exists”就是“也许火星上过去有生命形式的存在”的原因。
单选题 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】 C
【答案解析】[解析] 事实细节题。第二段第一句意为“有人相信，如果产生适当的环境，火星就能容纳生命”。这种适当的环境就是“聚集大气层中太阳的热量”使“火星变暖”。因此确定C为正确答案。
单选题 People may be able to live on the Mars ______.
A. within the next 200,000 years B. only 200,000 years from now
C. only 150,000 years from now D. as soon as the planet becomes cool enough
【正确答案】 A
【答案解析】[解析] 推理判断题。第二段中“据估计整个过程也许要用10万到20万年”。所以答案A正确。
单选题 The author's attitude towards the possibility of life on the Mars in the future is ______.
A. doubtful B. positive C. negative D. uninterested
【正确答案】 B
【答案解析】[解析] 推理判断题。要求判断作者对未来火星上有生命可能性的态度。第一段中作者表明火星上有流水的痕迹，两极有冰，有些科学家认为火星上曾经有生命存在。第二段作者分析了未来火星上生活的可能性。因此可以判断答案为B。
单选题 Which is the best title for this passage?
A. The Possibility of Life on the Mars B. Future Conditions on the Mars
C. The Mars and the Earth D. A Study of the Climate of the Mars
【正确答案】 A
【答案解析】[解析] 主旨大意题。通观全篇文章，作者讲述了在火星上生活的可能性。所以选项A为正确答案。