Final answer:
A problem and solution map is the best choice to depict the pay inequity between black and white soldiers and the correction of this problem by Congress.
Step-by-step explanation:
The best graphic organizer to illustrate the first paragraph of the passage, which describes the pay disparities between black and white soldiers during the Civil War and the subsequent correction of this inequity by Congress, would be (d) A problem and solution map. This organizer effectively showcases the issue at hand—the unequal pay—and the solution that was later implemented—equal pay and back pay for black soldiers. It allows for a clear depiction of the initial situation, the challenges faced by African American troops, and the resolution that rectified the wage discrimination.