Why Was the Supreme Court's Ruling in Plessy V

Why was the Supreme Court's ruling in Plessy v. Ferguson so significant?

A) It banned segregation in the public schools.
B) Segregation was permitted on the basis of establishing "separate but equal" facilities.
C) Only railroads that did not cross state-lines were permitted to segregate.
D) The unanimous decision declared the amendments outlawing slavery had been improperly passed.
E) Interracial marriages were prohibited.