Population tends 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 every day for one month. After the first week, you would have only 64 cents, but after the fourth week you would have over a 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 repents(缓慢进行)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 1975 world population reached 4 billion, which is another billion people in only fifteen years.
World population is increasing at a rate of 9000 per hour, 220000 per day, and 80 million per year. This is not only due to higher birth rate, but to lower death rate as well. The number of births has not declined at the same rate as the number of deaths.
Some countries, such as Columbia, Thailand, Morocco, Costa Rica, and the Philippines, are doubling their population about every twenty-one years, with a growth rate of 3.3% a year or more. The United States is doubling its population about very eighty-seven years, with a rate of 0.8% 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.
This passage chiefly discusses______.
A.the growth of world population
B.one type of the exponential rate
C.the population problem of more rapidly growing countries
D.the possible ways of dealing with the rapid population growth
第1题
口蹄疫疫苗与高致病性猪蓝耳病灭活疫苗的接种间隔时间应在_ 天以上。
A.7
B.10
C.16
D.18
第3题
口蹄疫疫苗与高致病性猪蓝耳病灭活疫苗的接种间隔时间至少应在()天以上。
A.7
B.10
C.16
D.18
第4题
国家对生猪实施强制免疫的动物疫病种类有()。
A.口蹄疫
B.口蹄疫、猪瘟
C.口蹄疫、高致病性猪蓝耳病、猪瘟
D.口蹄疫、猪蓝耳病、猪瘟、伪狂犬病
第7题
虎斑心、橡皮肺、盲肠 “钮扣状”溃疡分别是()的较典型病理特征。
A.猪瘟、口蹄疫、高致病性猪蓝耳病
B.高致病性猪蓝耳病、口蹄疫、猪瘟
C.口蹄疫、高致病性猪蓝耳病、猪瘟
D.口蹄疫、猪瘟、高致病性猪蓝耳病
第8题
我国猪高热病的病原是()
A.蓝耳病病毒
B.高致病性的蓝耳病病毒
C.变异的蓝耳病病毒
D.欧洲型蓝耳病病毒
E.美洲型蓝耳病病毒
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