Why was it necessary for Congress to pass the 15th Amendment even though the 14th Amendment gave equal citizenship to African Americans?

Abecause the 14th Amendment did away with the poll tax and literacy test

Bbecause the 14th Amendment prohibited the practice of slavery in all states

Cbecause the 14th Amendment did not specifically protect African Americans' voting rights

Dbecause the 14th Amendment did not allow the Southern states to secede the Union