Answer:
The Fifteenth Amendment was necessary because despite their citizenship, African Americans were legally prohibited from voting in some states. Option C, "Despite their citizenship, African Americans were legally prohibited from voting in some states," is the correct answer. The amendment was introduced to address the issue of racial discrimination and ensure that the right to vote could not be denied or abridged based on race, color, or previous condition of servitude. It aimed to provide African Americans, particularly former slaves, with the legal protection and recognition of their voting rights that had been denied to them through various discriminatory practices, such as poll taxes, literacy tests, and other voter suppression tactics.