it ha been etimated that a thouand year ago there were le than 400 million people on earth。 today， however， the world＇ population ha amounted to 5，000 million。 what i wore， it keep growing at a urpriing peed。 if thi trend continue， the world＇ population will hoot up to 7，000 million by the year xx。 thi i what we call population exploion。
the rapid development of cience and technology i the main caue of population exploion。 we can ee that the population ha been growing at a tremendou peed ince the indutrial and agriculture revolution in 1650， which raied the people＇ tandard of living， and the emergence of modern medicine in 1550， which lowered the people＇ death rate。
population exploion will reult in a lot of uch problem a food hortage， houing hortage and unemployment。 it i time that we acted quickly to carry out the policy of birth control otherwie， man＇ urvival on the earth will be threatened。