How long can human beings live? Most scientists who study old age think that the human body is1to live no longer than 120 years. However, 110 years is probably the longest that anyone could hope to live -- if he or she is2healthy and lucky. Some scientists even say we can live as long as 130 years! Yet, our cells simply cannot continue to reproduce3. They wear out, and as a result, we get old and4die.
Even though we can't live forever, we are living a5life than ever before. In 1900, the average American life span (寿命) was only 47 years, but today it is 75 years!

When does old age begin then? Sixty-five may be out-of-date as the6line between middle age and old age. After all, many older people don't begin to experience physical and mental7until after age 75.
People are living longer because more people8childhood. Before modern medicine changed the laws of nature, many children died of common childhood9. Now that the chances of dying10are much lower, the chances of living long are much higher due to better diets and health care.

On the whole, our population is getting older. The11in our population will have lasting effects on our social development and our way of life. Some people fear such changes will be for the worse, while some see12, not disaster, many men and women in their "golden years" are healthy, still active, and young in13if not in age.
As the society grows old, we need the14of our older citizens. With long lives ahead of them, they need to15active and devoted.

1．	A． designed B． selected C． improved D． discovered

2．	A． completely B． generally C． apparently D． extremely

3．	A． rapidly B． harmlessly C． endlessly D． separately

4．	A． eventually B． hopelessly C． automatically D． desperately

5．	A． busier B． longer C． richer D． happier

6．	A． finishing B． guiding C． waiting D． dividing

7．	A． stress B． damage C． decline D． failure

8．	A． survive B． enjoy C． remember D． value

9．	A． problems B． fears C． worries D． diseases

10．	A． poor B． young C． sick D． quiet

11．	A． changes B． recovery C． safety D． increases

12．	A． dreams B． chances C． strengths D． choices

13．	A． mind B． appearance C． voice D． movement

14．	A． protection B． suggestions C． contributions D． permission

15．	A． sound B． appear C． turn D． stay