The use of sit-down strikes to promote change in the workplace was MOST associated with the Industrial Workers of the World. Option C is correct.
A sit-down strike is a labour strike and a kind of civil disobedience in which an organized group of workers, generally working at factories or similar centralized locations, take unauthorized or illegal possession of the place where they work by "sitting down" at their stations in order to prevent employers from replacing them with strikebreakers.