A Southern Route for the Transcontinental Railroad Seemed the Best

A southern route for the transcontinental railroad seemed the best because

A) northern areas were all organized territories.
B) slave labor could be used to construct it.
C) the railroad would be easier to build along the proposed southern route because of the topography and the proposed southern route would pass through either existing states or organized territories.
D) Mexican leader Santa Anna agreed to contribute money for the project.
E) it would firmly tie southern California to the Union.