小编整理老托福考试听力PartC精选第73期,包括英文原文+音频,考生们不妨练习一下。更多托福备考信息尽在智课网托福频道!

  Look at our topographical map and you'll see that the middle third of the North American continent from the Rocky Mountains almost to the Mississippi River is pretty flat. This is the Great Plains. This kind of area is sometimes called a prairie, sometimes a steppe. That's s-t-e-p-p-e. The defining features are level terrain, dry climate, and an absence of trees. The Great Plains are actually the former bed of a shallow inland sea. Over millions of years, sediment left by glaciers, water, and wind smoothed out the dry sea bed. As I said, the Great Plaints are bordered on the west by the Rocky Mountains. And it's really the Rockies that are responsible for the formation of the grasslands. The mountains are so high that they block the heavy moist air traveling eastward form the Pacific Ocean. Lighter, drier air passes over the mountains. Until people intervened with irrigation and farms, only grass could grow on the dry, windy plain. In fact, we can divide the Great Plains into three zones. In the west, where it's driest and windiest, the grass is very short. In the eastern zone, there's more rain and grass grows as high as 360 centimeters. In the middle third, there's a mix of grass species that grow to an intermediate height.

  【生词摘录】

  1. topographical: adj. 地形学的

  2. prairie: n. [C]大草原,牧场

  3. steppe: n. [C]大草原,干草原

  4. level: adj. 平坦的

  5. terrain: n. 地形

  6. sediment: n. [C]沉淀物

  7. glacier: n. [C]冰川

  8. smooth out: v. 消除,使平滑

  9. moist: n. [C]潮湿

  10. intervene: v. 介入,干预

  11. windy: adj. 多风的

  12. intermediate: adj. 中间的

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