Cheap land in the West, new farm machinery, and the growth of railroads lead to Bonanza farms. Option B is correct.
Bonanza farms constituted very large farms established in the western United States during the late nineteenth century. They conducted large-scale operations, mostly cultivating and harvesting wheat. Numerous factors resulted in the developing of Bonanza farms such as the efficient new farming machinery of the 1870s, cheap abundant land available during that period, the growth of eastern markets in the U.S., and completion of most major railroads between the farming areas and markets.