C) The doctrine of "separate but equal" was allowed to continue
In 1892, Homer Plessy, a black man, sitted in a "whites only" car of a Louisiana train. Louisiana had a Separate Car Act (1890), which required separate railway cars for blacks and whites. Plessy ended up arrested.
In the case, Plessy’s lawyers argued that the Separate Car Act violated the 13th and 14th Amendments, which established absolute equality for the races before the law.
However, the Supreme Court considered that segregation didn't imply the inferiority of African Americans, and wasn't discrimination. Therefore, the doctrine of "separate but equal" was allowed to continue.