C. winning the Brown v. Board of Education Supreme Court case.
Explanation:
Thoroughgood Marshall was a civil rights activist, lawyer, and justice associate of the Supreme Court (1967–91)of the United States. he was the first person from the African American community to hold that position of the Court. Nevertheless, it was the victory of Marshall before the Supreme Court in Brown v. Topeka's Board of Education that built his credibility as a powerful and innovative legal adversary and proponent of social change. The ruling of the case declared racial segregation in American schools as unconstitutional.
