From "Appeal to Congress for Impartial Suffrage" How does Douglass support his claim that African Americans have rendered a "score of past services" to the United States?

А. by noting that the economy has greatly benefited from African- Americans' labor

В. by citing the community improvements that have resulted from African-Americans' charitable activities

C. by stating that African Americans refused to complain to Congress about their suffering

D. by observing that African Americans fought with white Union soldiers during the Civil War​