Level4 Unit1 Part1 Landforms  地貌地形

Mountains are landforms higher than 2000feet, or about 600 meters, above sea level.

Hills are like mountains, but as tall.

Mountains are formed by forces deep withinthe earth and are made of many types of rocks.

Rivers are streams of water that usuallybegin in mountains and flow into the sea.

Many early cities were built alongsiderivers.

Most of the world's water is in the oceans,which are large bodies of salt water.

The oceans are also an important source ofoxygen.

Deserts are areas of land that receive littleor no rainfall.

The amount of rainfall in some deserts is solow that only a few plants can survive.

A valley is a low, relatively flat areabetween hills or mountains, often with a river running through it.

Some valleys are formed by flowing water, andother are formed by glaciers.