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。