it has been estimated that a thousand years ago there were less than 400 million people on earth. today, however, the world's population has amounted to 5,000 million. what is worse, it keeps growing at a surprising speed. if this trend continues, the world's population will shoot up to 7,000 million by the year . this is what we call population explosion.

　　the rapid development of science and technology is the main cause of population explosion. we can see that the population has been growing at a tremendous speed since the industrial and agriculture revolution in 1650, which raised the people's standard of living, and the emergence of modern medicine in 1550, which lowered the people's death rate.

　　population explosion will result in a lot of such problems as food shortage, housing shortage and unemployment. it is time that we acted quickly to carry out the policy of birth control otherwise, man's survival on the earth will be threatened.