The correct answers are B) Many enlisted and wanted to make an important contribution to the Union cause and C) They served as cooks, nurses, ironsmiths, etc.
African American soldiers helped the Union cause in that many enlisted and wanted to make an important contribution to the Union cause, and they served as cooks, nurses, ironsmiths, etc.
Once the Civil War had started, President Abraham Lincoln considered the idea to allow black men to enlist in the Union Army. With the signing of the Second Confiscation and Militia Act of July 17, 1862, the President was allowed to invite all kinds of people that could serve the army during the war. That is how African Americans enlisted in the Union's Army.