What Was the Basis for the Supreme Court's Decision in Plessy

What was the basis for the Supreme Court's decision in Plessy v.Ferguson (1896) that upheld the constitutionality of a state law requiring segregated railroad facilities?

A) Former slaves are not entitled to full citizenship rights because they did not immigrate to the United States willingly.
B) Former slaves are not entitled to full citizenship rights because they were considered property under the law.-
C) The Constitution does not prohibit segregation;it only mandates equal protection under the law.
D) Railroad transportation involves interstate commerce,which is regulated by Congress;there is no provision in federal law that prohibits segregation.