The correct answer is - D. Culture revolution.
The Culture Revolution, or officially the Great Proletarian Culture Revolution, in China, was taking place from 1966 to 1976. The purpose of it was that Mao Zedong manages to strengthen his position again, because he lost on support after the terrible Great Leap Forward when millions of Chinese people died.
The principal used to strengthen his position again, was to eliminate all the people that were conspiring against the Communist Party, all the critics, and all the people that wanted to country to move away from communism and turn into capitalism.
The end result was lot of death by torture and killing, when pretty much everyone that had different views and it was known about it, was eliminated.