INTRODUCTION Human population in the past 48 years has more than doubled its seize, from 2.5 billion in 1950 to 5.9 billion in 1998 . A few month ago the Secrtary of the United Nation declared a baby as the No. 6 billion citezen of the earth. As you may have noticed, human population has reached a size that threatened our environment and the sustainability of the earth. Is the earth bounded to face this number of human? In fact, in the …showed first 75 words of 1464 total…

…showed last 75 words of 1464 total…