2. 外语
  3. Populations tend to grow at an exponential (指数的) rate. This means that they progressively double. As an example of this type of

Populations tend to grow at an exponential (指数的) rate. This means that they progressively double. As an example of this type of

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问题     Populations tend to grow at an exponential (指数的) rate. This means that they progressively double. As an example of this type of growth rate, take one penny and double it every day for one month. After the first week you would have only 64 cents, but after the fourth week you would have over million dollars.
    This helps explain why the population has come on "all of a sudden". It took from the beginning of human life to the year 1830 for the population of the earth to reach one billion. That represents a time span of at least two million years. Then it took from 1830 to 1930 for world population to reach 2 billion. The next billion was added by 1960, only thirty years, and in 1979 world population reached 4 billion, which is another billion people in only fifteen years.
    World population is increasing at a rate of 9 000 per hour, 220 000 per day, 80 million per year. This is not only due to high birth rates, but to lower death rates as well. The number of births has not declined at the same rate as the number of deaths.
    Some countries, such as Colombia, Thailand, Morocco, Costa Rica, and the Philippines, are doubling their populations about every twenty-one years, with a growth rate of 3. 3 percent a year or more. The United States is doubling its population about every eighty-seven years, with a rate of 0. 8 percent per year. Every time a population doubles, the country involved needs twice as much of everything, including hospitals, schools, resources, food and medicines to care for its people, it is easy to see that this is very difficult to achieve for the more rapidly growing countries.
It took______for the world to increase its population from 1 billion to 4 billion.
选项 A、100 years
B、149 years
C、19 years
D、over two million years
答案B
解析 本题是一道根据具体细节推算类问题。问需要多长时问世界人口从10亿增加到了40亿。文章第二段指出，从有人类生活开始到1830年，地球上的人口达到10亿，这代表着至少200万年的一个时期。从1830年到1930年世界人口达到20亿；到1960年又增加了10亿人口，这仅有30年的时间；1979年世界人口达到40亿，这样，在15年期间又增加了10亿人。因此，本题的正确答案应是B：1979—1830=149年。
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