The correct answer is B) of the availability of farmland.
During the early 1800s, many people migrated westward in search of new opportunities, especially for farming and land ownership, as the availability of fertile land in the west was a major draw for settlers. The other options do not accurately reflect primary motivations for westward expansion during that time period. The Transcontinental Railroad was completed later in the 1860s, and while there were individuals escaping slavery, it was not a widespread motivation for westward migration compared to the desire for land.