What was one of thurgood marshall’s major achievements?

organizing the montgomery bus boycott

founding the national association for the advancement of colored people

winning the brown v. board of education supreme court case

defending the little rock nine

The correct answer is: "winning the Brown v. Board of Education Supreme Court case".

Brown v. Board of Education was a case that led to the enactment of a landmark decision by the US Supreme Court in 1954.  

The case was about the constitutionality of the "separate but equal" lemma that was accepted in a former decision enacted by the US Supreme Court in 1896 in the Plessy v. Ferguson case. Such decision allowed the proliferation of segregated schools under the belief that, if facilities were equal in quality, such education system was not violating the equality of rights provision that had been guaranteed for all US citizens by the Equal Protection Clause, included in the Reconstruction Amendments to the US Constitution.  

Brown v. Board of Education overturned the abovementioned previous Supreme Court decision and declared segregation unconstitutional. Thurgood Marshall (1908 – 1993) was the first African American justice in the US Supreme Court. He participated in the enactment of the landmark decision of Brown v. Board of Education.

letter d is correct.

a. always outside of government control.