What does the abbreviation ad mean

The sixth amendment of the u. s. constitution guarantees the right to which of the following?

How did african americans the union during the civil war? a. by serving as representatives in congress b. by enlisting in the military to fight c. by organizing massive slave revolts in the south d. by negotiating for peace with the confederacy

Was the civil war inevitable? could anything have been done through compromise to stop it, or did it have to happen?