Water
Water has three states----liquid, solid and gas. When its temperature gets lows than 0'C, it will freeze intoice and become a solid. And when water is heated to 100'C, it will form steam and become a gas. Therefore ice is the solid form of water and steam is water in the form of gas.
Water is very important to living things. Without water there could be no life on the earth. All animals and plants need water. Man also needs water. 65 percent of our body is water, and 85 percent of our blood is water, too. Maybe we could live 80 days without food. But we could live only ten days without water.
Unfortunately, water has now been polluted by rnan. Poisonous chernicals and industrial waste have been dumped into river, lakes and oceans, making water dirty everywhere in the world. Although about 70 percent of the earth are covered with water, there are many places in the world still running out of water. As the famous lines goes:
Water, water, everywhere, No any drop to drink.
So we should take drastic measures to deal with this problem so as to avoid a serious worldwide water shortage in the future.
文章第一段展开写水所具有的三种状态，没有涉及到什么高深的科学术语，简简单单几句话就介绍了水在什么情况下呈什么状态：第二段用举例的方法写水对生物的重要性，所举的都是日常生活中常见的例子——植物、动物需要水，人也离不开水；第三段转折到水的污染上来，这里用的也是举例法，选择了工业污水这个典型的例子。最后的结尾提出了建议。 |