数组Q[0..n-1]作为一个环形队列，f为当前队头元素的前一位置，r为队尾元素的位置，假定队列中元素的个数总小于n，队列中元素的个数是()。
A. r-f
B. n+f-r
C. n+r-f
D. (n+r-f)modn
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But eighty or even ninety...normal life-span for humans(paragraph 3) is closet in meaning to
A. on average, people now live to be over eighty.
B. we should recognize that people now live to between eighty and ninety on average.
C. nowadays it isn't normal for people to die younger than eighty.
D. average life expectancy is increasingly being considered to be eighty or more.
In paragraph 3, which of the following is NOT given as a reason for a reduction in death rates？
A. New inventions.
Better hygiene.
C. Improved food production.
D. Better control of fatal diseases.
The author seems to believe that status syndrome may be cured
A. if the measures can actually weaken the relationship between social position and health.
B. if the government shouts louder in their campaign against diseases resulting from unhealthy habits.
C. if the government helps people find a stronger will power to give up their unhealthy habits.
D. ff the government undertakes bigger and more effective ad campaigns against poor education.
Which of the following recommendations might be made by the author？
A. Increasing food and industrial production, and encouraging people in undeveloped countries to have fewer children.
B. Improving education about the environment and banning the export of wood products from poor to rich countries.
C. Encouraging people worldwide to have fewer children and to behave in a more responsible way towards nature.
D. Restricting population worldwide and increasing the use of nonrenewable resources.
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