Why Was It Necessary to Add the Thirteenth,Fourteenth,and Fifteenth Amendments

Why was it necessary to add the Thirteenth,Fourteenth,and Fifteenth Amendments to the U.S.Constitution following the Civil War?

A) The Constitution outlawed the federal government's interference with state laws.
B) The Bill of Rights gave state laws precedence over federal laws.
C) The Constitution had condoned slavery and allowed states to set voting requirements.
D) They weren't necessary;they were passed merely for emphasis and propaganda.