The most important features in the growth of American economy in the early 20th cenruty were（）
- Athe use of steam and electricity as chief energy,the development of lare corporation and the development of railway
- Bthe development of large corporation,urbanization and the employment in production of new technology
- Cthe appearance of airplane,the use of electricity on a large scale and urbanization
- Dthe rapid development of industry,railway and large citie