题目内容：
Doctors are of the opinion that most people cannot live beyond 100 years, but a growing number of scientists believe that the aging process can be controlled. There are more than 12,000 Americans over 100 years old, and their numbers are increasing each year. Dr. James Langley of Chicago claims that, theoretically and under ideal conditions, animals, including man, can live six times longer than their normal period of growth.
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