How did Guinn and Beal v. United States (1915) affect voters' rights?
a) It expanded 15th Amendment rights by giving all citizens the right to vote.
b) It limited 15th Amendment rights by supporting the use of literacy tests for voters.
c) It clarified 15th Amendment rights by ending a state restriction on minority voting rights.
d) It restricted 15th Amendment rights by allowing state regulation regarding voter requirements.
