課堂翻譯二 54、55-1-1

The hydrologic cycle,or watwe cycle, collects, purifies, and distributes the earth's fixed supply of water as Figus 3-18.Water is an amazing substance (Science Focus, at right), which makes the water cycle critical to life on earth.
The water cycle is powered by energy from the sun,which causes evaporation of water from the oceans, lakes, rivers, and soil. Evaporation changes liquid water to water vapor in the atmosphere, and gravity draws the water back to the earth's suriace as precipitation(rain, snow, sleet, and dew). About 84% of water vapor in the atmosphere cimes from the oceans; the rest comes from land. Over land, about90% of the water that reaches the atmosphere evaporates from the surfaces of plants through a process called transpiration.

水文循環和水循環，這兩個循環分別收集、淨化和分配地球上所固定供給的水(圖請參考課本P54)。水是很奇特的物質它是水循環中不可或缺之物質在我們所生存的地球上。
水循環的動力是靠太陽蒸發水於海洋、湖泊、河流或土壤中。蒸發的水便水蒸氣於大氣中，受地心引力的影響，這些水變成與水或雪等降下於地表上。而84%的水汽是由海洋來的其餘則是陸地來的。在陸地上90%的水汽是由水穿透於植物的表面而來的，這個過程我們叫蒸騰作用。