The most important features in the growth of American economy in the early 20th cenruty were（）

• A、the use of steam and electricity as chief energy,the development of lare corporation and the development of railway
• B、the development of large corporation,urbanization and the employment in production of new technology
• C、the appearance of airplane,the use of electricity on a large scale and urbanization
• D、the rapid development of industry,railway and large cities