阅读下列文段，完成后面练习题：

    彗星主要是由冰构成的──水（H2O）冰，还有少量的甲烷（CH4）冰和一些氨（NH3）冰。在撞击地球的大气层时，一个中等大小的彗星碎片会产生一个白炽的火球和一种巨大的冲击波。火球会烧毁树木，冲击波会扫平森林，它的声音还会波及全球。但是这样的彗星不太可能在地上撞出一个环形山。彗星上的冰块在进人大气层的时候全部融化了，因此不会幽灵般地出现，这种现象令人不安地向人们关于宇宙是万古不变、井然有序这一观念进行挑战。如果那条天天随着星星起落的壮丽的乳白色光带是无缘无故地出现在那里，与人间世事毫无关系，那简直是不可思议的。因此出现了这样的观点：彗星是灾难的预兆，是神谴的预兆──它们预示了帝王的终日，王国的崩溃。对于彗星，巴比伦人认为是天髯，希腊人认为是垂发，阿拉伯人认为是燃烧的剑。在托勒密时代，人们根据彗星的形状把它们分类为“梁”、“喇叭”。“坛子”等。托勒密认为彗星给人类带来战争、炎热的气候和“动乱”。中世纪的一些彗星图看上去像未探明的飞行的十字架。一个名叫安德烈亚斯·西利奇厄斯的马格迪堡路德教主管人（即主教），在1578年发表了一篇题为“新彗星的科学启示”的文章。他在文章中。提出了一个独特的观点，他说彗星是“人类罪恶的浓烟，每天、每时、每刻都在升腾，它在上帝面前丑态百出、胆战心惊，逐渐地由浓烟形成长着卷发梳着辫子的彗星，最后被天国最高法官的怒火烧着了”。但是另一些人反驳说，如果彗星是罪恶的浓烟的话，天空势必乌烟滚滚。

　　　　　　　　　　　　　　　　　　                                                                                       　──选自《宇宙的边疆》（第四章）

Every month, junior high schools in China choose one hero of the month. This person is a hero because he or she has done something to help protect animals in danger. Huang Jing decided to write a letter to the President of China.

Dear Mr. President,
I have been doing a project at school recently about animals in danger. I think the situation all over the world is really terrible. I am writing to you to suggest what China should do to help protect animals more.
I know that there are nearly 2,000 nature reserves in China, which is good. I live in Beijing and there are about 30 reserves outside the city. We visited one of them last month to see for ourselves.
I feel so sorry for the giant panda. It's one of the most popular animals in the world and a real symbol of China. We learned that pandas mainly live on bamboo, and that a panda can eat half its body weight of bamboo in 24 hours! That's a lot of bamboo. I think we should try to do more to stop cutting down forests. Pandas are already a rare animal and it would be so sad if they became extinct (灭绝) forever.
The other animal we should try to protect more is the Chinese alligator (扬子鳄). These creatures live in some parts of eastern China. These beautiful animals live in freshwater rivers and lakes but the water in some places isn’t clean enough for them to live in. It's really dirty in fact. The government should stop factories polluting the lakes and rivers.
If we protect these beautiful animals in China, more foreigners may wish to visit China to see them. They could be an important tourist attraction. It would be good if more people came to visit our beautiful country, especially to see the quieter areas in the country. Now most visitors just see the cities.
I hope you will encourage more people to think about such an important subject.
Sincerely yours,
Huang Jing

 汽车的散热器用水作冷却剂利用了水的____较大的性质；如果散热器中装有10kg的水，在温度升高10℃的过程中水吸收的热量相当于完全燃烧____ m³的天然气放出的热量．天然气的热值q=4.2×10⁷J/m³，水的比热容c_水=4.2×10³J/（kg•℃）．

用数轴表示某些化学知识直观、简明、易记。下列数轴表示错误的是（   ）