Ⅲ.阅读理解
The earth is the only planet that scientists think has life. Why does the earth have life while the other planets don't? For one thing, the earth is just the right temperature. As the_third_planet from the sun，the earth seems to be just the right distance away. The planets which are closer to the sun are so hot that their surfaces bake(烘烤)in the sun. The farthest planets are cold balls.
When the earth developed—which scientists believe may have happened about 4 billion years ago—many gases covered the earth. The gases caused the earth to be hot. But something wonderful happened. The temperature was just right for thick clouds to form. It rained very hard for a very long time. This gave the earth its oceans. Water made it possible for plants to grow. The plants created oxygen in the atmosphere. Oxygen is the gas that humans and animals breathe.
Only one other planet in the solar system seems to be something like the earth. That planet is Mars (火星). Mars is smaller than the earth，and it is quite a bit cooler. But it is not too cold for humans. On some days, the temperatures are as low as a winter day in the northern United States. If you wore a special spacesuit, you could walk around on Mars. You would have to bring your own air to breathe，because the air on Mars is too thin to breathe.
Mars has the largest volcano(火山)in the solar system. It is sixteen miles high. The highest volcano on the earth is five miles high. The most unexpected(未预料到的)sight on Mars is driedup river beds. Scientists believe that Mars was once much better than it is now. Does this mean there could have been living things on Mars? Scientists are not sure, but there has been no sign so far.
文章大意：文章介绍了地球存在生命的原因以及火星的情况。
1.Which of the following is NOT the reason that the earth has life?
A.The earth is just the right temperature.
B.The volcanos on the earth are lower than those on Mars.
C.There is oxygen in the atmosphere of the earth.
D.The earth seems to be just the right distance away from the sun.
答案：B 细节理解题。文中提到地球是可证实的唯一有生命存在的太阳系行星，其原因包括地球温度合适、距太阳距离适中和大气里含有氧气等。B项火山与此无关。
2.The underlined phrase“the third planet”in the first paragraph refers to________.
A.the Sun B.the Moon
C.the Earth D.the Mars
答案：C 词义猜测题。根据第一段中内容可知距离太阳第三远的行星指的是地球。
3.Which of the following about the Mars is NOT true?
A.There could have been living things on Mars.
B.Mars has the largest volcano in the solar system.
C.There is almost no oxygen in the air on Mars.
D.Mars is smaller than the earth，and it is quite a bit cooler.
答案：A 细节理解题。文章最后一段提到火星上有干涸的河床的迹象，但这一点并不能证实火星上存在生命，因为还没有生命迹象，故A项不正确。其他三项都与文章相符。
4.Which of the following is probably the best title for the passage?
A.The Earth
B.The Moon
C.Planets in the Solar System
D.Mars is Most Like the Earth
答案：D 主旨大意题。文章先说明地球上存在生命的原因又对比了火星和地球，说明火星是与地球最相似的行星。D项做标题最为恰当。
