Students cover different parts of a cartoon human body with red or green pieces of paper during a lesson in sex education at a primary school affiliated with the Shanghai University of Science and Technology, Oct 24, 2011. [Photo/CFP]

Students are taught to recognize reproductive organs and sensitive areas in a sex education class at a primary school affiliated with the Shanghai University of Science and Technology, Oct 24, 2011. They held up "red lights" or "green lights" when they see offensive or friendly gestures in pictures displayed by the teacher. [Photo/CFP]