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

A) because the 14th Amendment did away with the poll tax and literacy test
B) because the 14th Amendment prohibited the practice of slavery in all states
C) because the 14th Amendment did not specifically protect African Americans' voting rights
D) because the 14th Amendment did not allow the Southern states to secede the Union