What was the connection between the gadsden purchase and the southern railroad route?

The Gadsden Purchase was a transaction that followed the conquest of much of northern Mexico by the United States. Its relationship to the transcontinental railroad is that  it was purchased because it was the most practical route  for the transcontinental railroad.  The purchase was negotiated by the U.S. minister to Mexico, James Gadsden.

c.

worked constantly and gave many sincere speeches about the importance of independence

answer; people where able to travel across the u.s.a faster than any other mode of transportation,travel time was about a week,from coast to coast