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the water cycle is powered by energy from the sun,which causes evaporation of water from the oceans,lakes,rivers,and soil.evaporation changes liquied water to water vapor in the atmosphere,and gravity draws the water back to the earth's surface as precipitation(rain,sleet,snow and dew).about 84% of water vapor in the atmosphere comes from the oceans;the rest comes from land.over land,about 90% of the water that reaches the atmosphere evaporates from the surfaces of plants through a process called transpiration.

水循環的能量來自太陽,造成水從海洋蒸發. 蒸發使液態水變成大氣中的蒸氣,降水是利用重力拖著水回到地球表面.大氣中約84%的水氣來自海洋,剩餘的來自陸地.陸地上約90%的水來自葉子 表面蒸發的水氣,此過程稱蒸散作用.