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  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.
When a population doubles, the country involved needs twice as much of everything, including
选项 A、hospitals and medicines
B、schools and students
C、food and manpower resources
D、all of the above
答案A
解析 本题问随着人口的加倍，相关国家各种需要也会翻倍，这些需要包括什么。文章最后一段最后两句话指出，人口每翻一番，这些国家就需要增加一倍各方面的需求，其中包括：医院、学校、资源、食品及人们保健所需要的药品。显然，这对于人口迅速增长的国家来说是很难办到的。因此，本题的正确答案应是A“医院和药品”。
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