2 . How long can human beings live? Most scientists who study old age think that the human body is ________ to live no longer than 120 years. However, 110 years is probably the longest that anyone could hope to live —— if he or she is ________ healthy and lucky. Some scientists even say we can live as long as 130 years! Yet, our cells simply cannot continue to reproduce ________. They wear out, and as a result, we get old and ________ die.

Even though we can’t live forever, we are living a ________ life 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 Sixty-five may be out-of-date as the ________ line between middle age and old age. After all, many older people don’t begin to experience physical and mental ________ until after age 75.

People are living longer because more people ________ childhood. Before modern medicine changed the laws of nature, many children died of common childhood ________. Now that the chances of dying ________ are 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. The ________ in 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 see ________, not disaster, many men and women in their “golden years” are healthy, still active, and young in ________ if not in age.

As the society grows old, we need the ________ of our older citizens. With long lives ahead of them, they need to ________ active and devoted.