Why did the boycott succeed? Were the actions of both the citizens of Montgomery as well as those of the U. S. Supreme Court necessary for its success?

It succeeded because it brought about the court ruling which says any racially segregated law is unconstitutional.

The actions of both the citizens of Montgomery as well as those of the U.S. Supreme Court necessary for its success because the people helped solve a lot of problems associated with unfair treatment of the Black- Americans and the court ruling on the matter ensured it being strictly adhered to avoid punishment.

d is the best answer for this question.