TOEFL Reading: ETS-TOEFL阅读机经 - N3BX33I4LEG8G3Z4L$

main idea. A. Until the late eighteenth century, farmers were limited to selling their crops and animal products for cash in nearby towns. B. Starting in the late eighteenth century, farmers increasingly produced crops for sale in domestic and international markets. C. Many farmers sold their products in order to be able to pay their taxes in cash and buy consumer goods for themselves. D. Railroads changed the way farming was done, since they brought modern tools from towns to the agricultural areas. E. Increased productivity resulted more from the cultivation of additional land than from the use of new tools and intensive agricultural processes. F. Farming was concentrated in river basins throughout the nineteenth century, while interior areas were devoted to pastureland for animals.