Chinese high school students have the longest study hours compared to their peers in Japan , the US  and South Korea. A survey conducted by the four countries said. The survey, released by the China Youth and Children Research Center on Monday, was jointly conducted with instructions in the four countries in September-October of 2008. It covers nearly 4,000 students in senior schools and vocational high schools in the four countries. About 78.3 percent of Chinese students said they spend more than eight hours at school and 56.7 percent said they study at least two more hours each day at home .by contrast, only 24.7 percent of their peers in the US , 20.5percent in Japan and 15.4 in Korea study more than two hour s after school. Around 60 percent of all students surveyed said their burden for studies was the heaviest. However the Japanese felt their burden was the worst with respondents   reaching 79.2 percent Among the five biggest headaches for young people in the four countries were: 0ver-sheduling ranked first, followed by a boring leisure life, unsatisfied appearance, little time for exercise and making friends, and no spare money "Moderate study pressure can better drive students to develop, however, too much will press their development space, and can even cause harm to their physical and psychological health" the survey said "Balancing their studies and all round development is a very important task" it said. Which of the following is not true about the survey?
it took about two months. it was conducted in four countries. Nearly 4,000 students took part in it. it was done only in senior high schools.