Why was the Brown v Board of Education known as such a landmark case in 1954?

A.)It was a case that said it was illegal to have Mexican-Americans sitting in class with "Whites"

B.)It was a case that ruled religion trumps state education

C.)It was a case that established "separate but equal" in public school was unconstitutional

D.)It was a case that ruled that segregation is legal in all 50 states