In the 20th century, machines are run mostly by electricity. Two hundred years ago electricity was not in common use. Machines were often run by water, and therefore many factories grew up by running rivers. Today, however, factories can be placed far from our rivers. 在20世纪，机器大都是电动的。两百年前，电还没有广泛的应用，机器都是靠水力发动，因此，工厂都是开在流动的江河边。然而，现今的工厂可以开在远离河流的地方。 编辑推荐：2009年下半年公共英语考试报名汇总 名师指导公共英语阅读考试技巧 公共英语pets三级全真模拟试卷 公共英语pets二级语法讲解汇总