A、its growing birth rates B、the migration of persons from other countries C、its good health condition D、its longer life expectan

Interviewer: As we all know, more people have been added to the Earth’s population in the 20th century than at any other time in human history. A report shows that "In 1900, just 100 years ago, the world’s human population numbered two billion people. Today, the total human population has grown three times as large and is now over six billion people." That sounds unbelievable. Dr. Baker, you are the expert on demography. Do you think it’s very serious?
Dr. Baker: Yes, absolutely serious. You know, the rate of population growth has gone up, the Earth adds one billion more people every 14 years, If this continues, the world’s population will double in the next century, nearing 12 billion in the year 2100. Our planet truly is becoming a more crowded place to live.
Interviewer: Then, what happened over the past 200 years to create such a rapid surge in the number of people living in the world?
Dr. Baker: We can’t explain it in one word. There are a few simple ideas that lie behind these trends.
Interviewer: Oh, can you explain it with more details?
Dr. Baker: O.K. You know, before 1900, many children who were born did not reach adulthood so they never had their own children. In America and Europe, young children died of many diseases that we now immunize against, such as diphtheria, tetanus, measles, pneumonia and whooping cough. In the 20th century, as these diseases became less common, more children lived to adulthood. The result was that more children than ever before were born and lived and had their own children, all of which increased the size of the world’s population. At the same time, people are also living longer. For example, in the U.S. the average life expectancy in 1950 was 57 years. Now people, on average, can expect to live 77 years, and this means that more people are living together on Earth at the same time.
Interviewer: What about the population in developing countries? Do their populations contribute to the population growth also?
Dr. Baker: Yes, that’s one of the main sources of the growth. In the latter part of the 20th century, people in other parts of the world -- Africa, Asia, South America and the Middle East -- who had traditionally lost many children to diseases, began to catch up with the health practices such as immunizing children that also allowed more children to live. As these children grew to adulthood they too started their own families and this also has contributed to the world’s current population growth.
Interviewer: But here is the critical question: Will the Earth’s population continue to grow. as fast as the last 100 years?
Dr, Baker: No, there are signs that the population growth rates in some parts of the world have started to slow down. In Europe, America, and in parts of Asia and Australia, most families are having less than two children. Some of these countries are actually experiencing negative population growth, meaning that their populations are growing smaller. In Russia, Eastern Europe, Germany and Northern Europe populations may actually shrink in size because people are having fewer and fewer children.
Interviewer: So, you mean America also has a shrinking population?
Dr, Baker: No, the Untied States will continue to grow. While birth rates in America have gone down -- primarily because of the migration of persons from other countries -- we will continue to have steady population growth. Today, the US has over 287 million people and is expected to grow to 400 million people by 2050,
Interviewer: So, that means we needn’t worry about the population growing too fast?
Dr. Baker: No, we can’t say that, cause there are also many parts of the world where population growth is still very high and populations are expanding rapidly.
Interviewer: For example?
Dr. Baker: For example, six countries account for one half of the population added every year: these are China, India, Pakistan, Bangladesh, Indonesia, and Nigeria.
Interviewer: Oh, yes, we know China has the largest population in the world.
Dr. Baker: Exactly, China alone has 1.3 billion people, but there is also India. India has slightly over 1 billion people, or about one sixth of the total world population. In countries where the rate of natural increase is approximately 2%, their population will double every 34 years. If population growth continues to be high in these and other countries, attempts to slow down the growth of the world population in the 21st century may well be futile.
Interviewer: But is it possible to slow down the growth in the long run?
Dr. Baker: Mm... it’s hard to say. Another issue is, even if people worldwide choose to have fewer children tomorrow, it will still take 50-60 years for the world’s population to stabilize, as there are so many people currently in their childbearing years. So, slowing the growth of the world’s population, even though this is happening in many parts of the world, may not be happening quickly enough. The world’s populations may still double again by the end of this century to 12 billion persons.
Interviewer: Oh, that doesn’t sound very good. Dr. Baker, what are we doing and what can we do to prevent overpopulation?
Dr. Baker: Er... that’s not easy to explain... Ah, since time is up, maybe we can continue the topic next time.
Interviewer: O.K. Thank you for your coming tonight.
Dr. Baker: My pleasure.