为什么稀混合气可以提高发动机燃料经济性？
参考答案：由于稀混合气中的汽油分子有更多的机会与空气中氧分子接触，容易燃烧完全，同时混合气越接近于空气循环，绝热指数越大，热效率随之提高；燃用稀混合气，由于其燃烧后最高温度降低，使汽缸壁传热损失较少，并使燃烧产物的离解减少，从而提高了热效率。另外，采用稀混合气，由于汽缸内压力、温度低，不易发生爆燃，则可以提高压缩比，增大混合气的膨胀比和温度，减少燃烧室残余废气量，因而可以提高燃油的能量利用效率。
Have you ever seen the man in the moon? If you look closely at the moon on some nights, you can see the face of the man in the moon. Some people say that they can see an old man carrying sticks.小题1: These pictures are made by the mountains and plains of the moon. Long ago people in England used to tell their children that the moon was made of green cheese.小题2: The moon is a large round rock. It is completely bare. There are no trees or plants on the moon. There are no rivers or seas. There are no living things. It never rains on the moon, and everything is covered with dirty, white dust. 小题3: When the sun shines on it, the moon is very hot, in the shade, however, it is as cold as ice.小题4: It does not weigh as much as the earth. If you went to the moon, you would weigh six times less than you do now. 小题5: 仔细阅读短文，将下面五句话还原到文中空白处，并将其标号填入答题栏的相应位置。
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