Interpreting practice：

　　The 20th century has seen the rise and decline of a succession of industries in the United States. The automobile industry has had to struggle to meet the challenge of foreign competition. Many new industries have appeared. Many of the currently rising industries are among what are known as high-tech industries, because of their dependence on the latest developments in technology.∥

　　High-tech industries tend to be highly automated and thus need fewer workers than traditional industries such as steel-making. As high-tech industries have grown and older industries have declined in recent years, the proportion of American workers employed in manufacturing has declined. Service industries—industries that sell a service rather than make a product—now dominate the economy.

　　20世纪以来，美国工业涨落不断。汽车工业不得不为迎接外国竞争的挑战而努力奋斗，出现了许多新工业。许我时新的工业都属于所谓的高科技工业，因为它们要依赖于科技上的最新发现。∥

　　高科技工业趋向高自动化，这样就比诸如炼钢这样的传统工业需要更少的工人。随着高科技工业的发展以及比较老的工业在近些年来的衰退，美国制造生产线上的工人比例已经下降服务行业——不制造产品而出售服务的行业——在经济中处于主导地位。