The answer is actually April 1969. The 9th CCP congress declared the cultural revolution was officially over. I understand the theory of it ending in 1976 due to the death of Mao. However key events in the ending of the C.R. had happened well before that. Such as the February crackdown (1967), "up to the mountains and down to the villages" campaign (1968-70) an the rustication campaign (1968). Good quiz on the whole though!!