Although all of the options prevented African Americans from voting on elections, the one who kept African Americas from nominating candidates for office was the option C.White primaries.
The White Primaries were southern laws of the Democratic party that blocked African Americans to voting on the primaries, prohibiting it. From 1896, along with the other disenfranchisement strategies (poll taxes, literacy tests and the Grandfather clauses), the White Primaries impeded the possibilities of the negro people from choosing a representative that would favor their causes; As in southern U.S the hardships for the African Americans were greater, a big amount of Black people would migrate to north and west, as we get to know as Great Migration.
The White Primaries was completely abolished only by the Voting Rights Act of 1965.