According to Oakes, what was Douglass’ main criticism of Lincoln after the North acknowledged the benefits of utilizing black soldiers?

a) Lincoln ignored that Black soldiers fought in segregated platoons.

b) Lincoln ignored that Black soldiers earned less pay and rations.

c) Lincoln was slow to establish a policy to punish Confederates for the mistreatment of Black prisoners of war.

d) Lincoln ignored that Black soldiers were being whipped by Union generals.