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 citie
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