Mountains are landforms higher than 2,000 feet or about 600 meters above sea level.山脉是海拔2000英尺或600米以上的地貌。
Hills are like mountains, but not as tall.山像山，但没有那么高。
Mountains are formed by forces deep within the Earth and are made of many types of rocks.山脉是由地球深处的力量形成的，由多种岩石构成。
Rivers are streams of water that usually begin at mountains and flow into the sea.河流是通常从山脉开始流入大海的水流。
Many early cities were built alongside rivers.许多早期的城市都建在河边。
Most of the world's water is in the oceans, which are large bodies of salt water.世界上大部分的水都在海洋中，海洋是大量的咸水。
The oceans are also an important source of oxygen.海洋也是氧气的重要来源。
Desserts are areas of land receive little or no rainfall.沙漠是很少或没有降雨的土地。
The amount of rainfall in some deserts is so low that only a few plants can survive.一些沙漠的降雨量很低，只有少数植物能存活。
A valley is a low, relatively flat area between hills or mountains, often with a river running through it.山谷是介于山丘或山脉之间的一个较低、相对平坦的地区，通常有一条河流流经山谷。
Some valleys are formed by flowing water, and others are formed by glaciers.一些山谷是由流水形成的，另一些则是由冰川形成的。
Many early civilizations developed near rivers.许多早期文明是在河边发展起来的。
Dessert temperatures can range from cold at night to very hot during the daytime, often above 120 degrees F.
The place where a river begins is its source.
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