???The agricultural revolution in the nineteenth century involved two things: the invention
of labor-saving machinery and the development of scientific agriculture. Labor-saving
machinery naturally appeared first where labor was scarce. "In Europe, said Thomas
Jefferson, "the object is to make the most of their land, labor being abundant: here it is to
make the most of our labor, land being abundant. It was in the United States, therefore,
that the great advances in nineteenth-century agricultural machinery first came.
??? At the opening of the century, with the exception of a crude plow, farmers could have
carried practically all of the existing agricultural implements on their backs; by 1860,
most of the machinery in use today had been designed in an early form. The most
important of the early inventions was the iron plow. As early as 1790 Charles Newbold
of New Jersey had been working on the idea of a cast-iron plow and spent his entire
fortune in introducing his invention. The farmers, however, were not interested in it,
claiming that the iron poisoned the soil and made the weeds grow. Nevertheless, many
people devoted their attention to the plow, until in 1869 James Oliver of South Bend,
Indiana, turned out the first chilled-steel plow.
1.What is the main topic of the passage?
(A) The need for agricultural advances to help feed a growing population
(B) The development of safer machines demanded by the labor movement
(C) Machinery that contributed to the agricultural revolution
(D) New Jersey as a leader in the agricultural revolution