We can begin our discussion of "population as a global issue" with what most person mean when they discuss " the population problem": too many people on earth and a too rapid increase in the number added each year. The facts are not in dispute. It was quite right to employ a similar matter that linked demographic growth to " a long, thin power fuse that burns steadily from time to time until it finally reaches the limit, and explodes". To understand the current situation, which is characterized by rapid increases in population, it is necessary to understand the history of population trends. Rapid growth is a comparatively recent phenomenon. Looking back at the 8,000 years of demographic history. We find that population have been really stable or growing very slightly for most of human history. For most of our ancestors, life was hard, often nasty, and very short. For most of human history, it was seldom the case that one in ten persons would live past forty, where infancy and childhood were especially risky periods. Often, societies were in clear danger of extinction because death rates could exceed their birth rates. Thus, the population problem throughout most of history was how to prevent extinction of the human race. This pattern is important to know. Not only does it put the current problems of demographic growth into a historical perspective, but it suggests that the cause of rapid increase in population in recent years is not a sudden enthusiasm for more children, but an improvement in the conditions that traditionally have caused high rate of death. Demographic history can be divided into two major periods: a time of long, slow growth which extended from about 8000B.C. till approximately 1650 A.D. And a period of rapid growth since 1650. In the first period of some 9,600 years, the population increased form some 8 million to 500 million in 1650. Between 1650 and the present, the population has increased from 500 million to more than 4 billion. And it is estimated that by the year 2020 there will be 8 billion people throughout the world. One way to appreciate this dramatic difference in such abstract numbers is to reduce the time frame to something that is more manageable. Between 8000B.C. and 1650, an average of only 50,000 persons was being added annually to the world's population each year. At present, this number is added very six hours. The increase is about 80,000,000 persons annually. The reason for a rapid growth of population lies in the fact that   _  .
people are permitted to have more children people can live better than before newborn babies die less than before we have found the secret of longevity
Question: We can begin our discussion of "population as a global issue" with what most person mean when they discuss " the population problem": too many people on earth and a too rapid increase in the number added each year. The facts are not in dispute. It was quite right to employ a similar matter that linked demographic growth to " a long, thin power fuse that burns steadily from time to time until it finally reaches the limit, and explodes". To understand the current situation, which is characterized by rapid increases in population, it is necessary to understand the history of population trends. Rapid growth is a comparatively recent phenomenon. Looking back at the 8,000 years of demographic history. We find that population have been really stable or growing very slightly for most of human history. For most of our ancestors, life was hard, often nasty, and very short. For most of human history, it was seldom the case that one in ten persons would live past forty, where infancy and childhood were especially risky periods. Often, societies were in clear danger of extinction because death rates could exceed their birth rates. Thus, the population problem throughout most of history was how to prevent extinction of the human race. This pattern is important to know. Not only does it put the current problems of demographic growth into a historical perspective, but it suggests that the cause of rapid increase in population in recent years is not a sudden enthusiasm for more children, but an improvement in the conditions that traditionally have caused high rate of death. Demographic history can be divided into two major periods: a time of long, slow growth which extended from about 8000B.C. till approximately 1650 A.D. And a period of rapid growth since 1650. In the first period of some 9,600 years, the population increased form some 8 million to 500 million in 1650. Between 1650 and the present, the population has increased from 500 million to more than 4 billion. And it is estimated that by the year 2020 there will be 8 billion people throughout the world. One way to appreciate this dramatic difference in such abstract numbers is to reduce the time frame to something that is more manageable. Between 8000B.C. and 1650, an average of only 50,000 persons was being added annually to the world's population each year. At present, this number is added very six hours. The increase is about 80,000,000 persons annually. The reason for a rapid growth of population lies in the fact that   _  .
A. people are permitted to have more children
B. people can live better than before
C. newborn babies die less than before
D. we have found the secret of longevity
Answer: