Answer:
B
Step-by-step explanation:
The United States paid Mexico $10 million for the Gadsden Purchase because they thought it would be the best place for a southern railroad route to the Pacific Ocean. Because the Rocky Mountains spanned across much of the U.S.'s territory in the West, they had limited options for building railroad routes. The area in the Gadsden Purchase was less mountainous, and a railroad was eventually built there.