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The full influence of mechanization began shortly after 1850, when a variety of machines came rapidly into use. The introduction of these machines frequently created rebellions by workers who were fearful that the machines would rob them of their work. Patrick Bell, in Scotland, and Cyrus McCormick, in United States, produced threshing machines. Improve- meats were made in plows to compensate for different soil types. Stream power came into use in 1860s on large farms. Hay rakes, hay-loaders, and various special harvesting machines were produced, Milking machines appeared. The internal-combustion engine run by gasoline became the chief power source for the farm.
In time, the number of certain farm machines that came into use skyrocketed and changed the nature of fanning. Be-tween 1940 and 1960, for example, 12 million horses and mules gave way to 5 million tractors. Tractors offer many. features that are attractive to farmers. There are, for example, numerous attachments: cultivators that can penetrate the s0il to varying depths, rotary hoes that chop weeds; spray devices that can spray pesticides in bands 100 feet across, and many others.
A piece of equipment has now been invented or adapted for virtually every laborious hand or animal operation On the farm. lathe United States, for example, cotton, tobacco, hay, and grain are planted, treated for pests and diseases, fertilized, cultivated and harvested by machine. Large devices shake fruit and nut from trees, gain and blend feed, and dry gain and hay. Equipment is now available to put just the right amount of fertilizer in just the right place, to spray an exact row width, and to count out, Space, and plant just the right number of seeds for a row.
Mechanization is not used in agriculture in many parts of Latin America, Africa, Agriculture innovation is accepted fastest where agriculture is already profitable and progressive. Some mechanization has reached the level of plantation agriculture in parts of the tropics, but even today much of that land is laboriously worked by people leading draft animals pal- ling primitive plows.
The problems of mechanization in some areas are not 0nly cultural in nature. For examples, tropical soils and crops differ markedly from those in temperate areas that the machines are designed for, so adaptations have to be made. But the greatest obstacle to mechanization is the fear in underdeveloped countries that the workers who are displaced by machines would not find work elsewhere, Introducing mechanization into such areas requires careful planning.
31. The first paragraph uses several examples to convey the ideas that______.

A. the introduction of machines into agricultural work created rebellions on the part of the farmers
B. the use of internal combustion engine as a chief power source for the farm produced great influence
C. the mechanization of agricultural work after 1850 gradually robbed many farmers of their work
D. ingenious improvements were made in fanning machines in the 1860s to yield production