The correct answer is D) After working for the NAACP and winning twenty-nine court cases, Marshall was appointed a Supreme Court justice.
Thurgood Marshall was a prominent lawyer for the NAACP. One of his most famous winning cases was the Brown vs. Board of Education Supreme Court case. In this case, Marshall argued that "separate but equal" public school facilities for blacks and white citizens was a clear violation of the Equal Protection clause of the 14th amendment. The court agreed and the Brown case lead to the end of segregated schools.
After his success in court cases like this, Marshall was appointed to the Supreme Court by president Lyndon B Johnson.