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 2000. This is what we call population explosion. The rapid developm...[繼續(xù)閱讀]