提高听力同时，你还可以了解到美国历史上的一些重要事件。请感兴趣的你一听为快吧！

<注意>国家大写
hints：the Great Plains
Farming was still America's main occupation. Scientists improved seeds. New machines did some of the work that men had done. American farmers produced enough grain, meat, cotton, and wool to ship the surplus overseas. The western regions still had room for exploration and for new settlements. Miners found ore and gold in mountains. Sheep farmers settled in river valleys. Food farmers settled on the Great Plains. Ranchers let their cattle graze on the vast grasslands. Cowboys drove great herds of cattle to the railroad to ship to the east. The "Wild West" pictured in many cowboy books and movies lasted only about 30 years.
农业仍然是美国的主要占领。科学家改良种子。新机器做了一些人做的工作。美国农民生产足够的粮食，肉类，棉花，羊毛乘船盈余海外。西部地区仍然有空间探索和新的定居点。矿工发现在山区的矿石和黄金。养羊农民在河谷定居。种食品农民落户在大平原上。牧场主让他们的牛吃草广大草原。牛仔赶着大批牛群到铁路乘船向东去。这幅“狂野西部”画出现在血多牛仔书籍和电影里历时仅约30年。