Which best describes the outcome of the 1913 case Guinn v. U.S.?

The outcome of the 1913 case Guinn v. U.S. was a significant ruling by the Supreme Court that declared the Grandfather Clause, used to disenfranchise African American voters in Oklahoma, unconstitutional. The Court found that the clause violated the Voting Rights Act of 1870 by effectively denying the right to vote based on race. This decision reinforced the legal challenges against discriminatory voting practices, although many such barriers persisted for decades.