The reason that the 15th amendment, passed in 1870, was partially unsuccessful was: a. mostly southern states failed to enforce it c. part of it was found to be unconstitutional b. mostly northern states failed to enforce it d. many states did not understand it

The reason that the 15th Amendment, passed in 1870, was partially unsuccessful was that A. mostly Southern states failed to enforce it.
The 15th Amendment stipulates that any person of age can vote, regardless of race and color. As you already know, the South really liked their slaves, and they were not willing to give them any form of freedom. 

That really sucks, but i don't know who your leader is, and i don't want to write that much