Answer:
d. the Homestead Act and the transcontinental railroad
Step-by-step explanation:
"With Federal resources focused on waging the war farther east, both native tribes and the Confederacy attempted to claim lands west of the Mississippi.
The Federal government's response included The Homestead Act and the construction of the transcontinental railroad. The goal was to encourage settlement, solidify Union control of the trans-Mississippi West, and further marginalize the physical and cultural presence of tribes native to the West."
Reference: National Park Service. “The War and Westward Movement.” National Parks Service, U.S. Department of the Interior, 2019