It is reported that the world’s population was 6 billion in the year 2,000,and it is growing faster and faster.The world’s population problem is the greatest one because it brings lots of problems,such as water resources problem,more and more people losing their jobs and so on.These problems are mainly in the developing countries because the population of the developing countries is over 4/ 5 of the world’s popuation.So China,the largest developing country,has kept the policy “one couple,one child.”