单选题 .  The agriculture 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 sufficient; here it is to make the most of our labor, land being abundant." It was in America, therefore, that the great advances in the nineteenth century agricultural machinery first came. At the opening of the century, with the exception of a crude (粗糙的) plow, farmers could have carried practically all of the existing agricultural tools 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 1890 Charles Newbolt 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, would home none of 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.  The word "here" in Line 4 refers to ______.