As is known to all, the world's poplulation is continueously to grow, which required enough amount of water to support.
With the rapid expanding of industrialization, plenty of toxic gas and liquid waste were produced, causing severe water pollution. Despite fresh water as it was, it can no longer be used. Until this time did people realize the importance of fresh water. If us human beings do not take action to protect the fresh water resources as soon as possible, no fresh water can be used someday in the future. What a terrible condition we would encounter then.
有些没按照你的来因为用你的话就完全不通顺了，还有最后一句（4）是什么鬼？