Why Did African American Men Choose to Enlist in the U.S

Why did African American men choose to enlist in the U.S. army to serve in the West after the Civil War?

A) They shared white Americans' disdain for Indians.
B) They wanted to prove their patriotism after emancipation.
C) They hoped to achieve a better quality of life.
D) They had a better chance of serving in an integrated unit in the West.