导读:

要求:
1.人们以为淡水是取之不尽的 (提示:雨水、河水、井水...)
2.实际上淡水非常紧缺的 (提示:人口增加,工业用水增加,污染...
3.我们应该怎么办
问题陈述 原因分析 建议措施

参考范文
Animals are essential in an ecosystem. But for various reasons the number of animals decreases to an alarming degree. All over the world, biological diversity has already become a key environmental issue.

Scientists from many fields generally attribute this phenomenon to three reasons. To begin with, human activities reduce the number of animals. For instance, the living areas of human beings enlarge gradually while the areas for animals shrink. As a result, animals die out. Next, natural evolutions also make some animals extinct. Moreover, some diseases among animals also cut the population of animals.

How to address this issue? Two approaches have been suggested. One is that humans should protect some rare animals. The other is that human must provide animals with a sound environment for them to survive and thrive.