新视野大学英语课件第二册Unit2-3
Nature has an __unchanging_ amount of water.Nature has a __perfect_ system of _recycling_ water.Water is _used_ again and again. It _falls_ as rain. Then it goes to one of three_places_. It might _sink_ slowly through the soil into the natural holding areas in the rock. _It might disappear into the air quickly_ by becoming vapor, or gas. ___It might run off into streams,rivers and oceans_. By itself, _nature can keep the balance and provide plenty of clean water for us__.
