The most important features in the growth of the American economy in the early 20th century were ___.
选项：

A:the use of steam and electricity as chief energy, the use of machines and the development of railway
B:the appearance of airplane, the use of electricity on a large scale and urbanization
C:the development of large corporation, urbanization and the application of new technology in production
D:the development of industry and large cities, the expansion of railroad network