Final answer:
The reaper and the steel plow revolutionized harvesting and cultivation processes in nineteenth-century agriculture, increasing farmers' output, improving farm production, and reducing the cost of food.
Step-by-step explanation:
The reaper and the steel plow were important for nineteenth-century agriculture because they revolutionized harvesting and cultivation processes. The reaper, invented by Cyrus McCormick, replaced the laborious process of cutting wheat by hand and greatly increased farmers' output. The steel plow, improved by James Oliver, made it easier to till the Midwestern terrain and improved farm production. These innovations allowed for larger quantities of crops to be produced, provided a more consistent quality of crops, and reduced the cost of food.