The only one of your choices that addresses your question is 'D', federal laws preventing voting. The reason being the laws that restricted voting were on the state level of government legislation not the federal level. The federal government ratified the 15th Amendment which extended suffrage (voting rights) to African Americans males in 1868, and the 19th Amendment extended suffrage to women in 1920. However after 1868 many state governments in the south began passing laws restricting the voting rights of African Americans, such restrictions included poll taxes and literacy tests. The Civil Rights Movement during the 1960's protested the voting restrictions legislated by state governments. In 1965 President Johnson signed The Voting Rights Act ending voter discrimination and federalizing voting rights. This piece of legislation is considered a landmark victory for the Civil Rights Movement. Also the 1960's saw the ratification of  the 24th Amendment which abolished poll taxes and literacy tests.