D should be the right answer. :)
Pioneer settlers were sometimes pulled west because they wanted to make a better living. Others received letters from friends or family members who had moved west. These letters often told about a good life on the frontier. The biggest factor that pulled pioneers west was the opportunity to buy land.
<span>uninhabitable deserts. It is the most frequently crossed international boundary in the world, with approximately 350 million legal crossings being made annually.</span>
