Samuel Preston, a sociologist at the University of Pennsylvania, studied how the American family is changing. He reported that by the time the average American couple reaches about 40 years of age, their parents are usually still alive. The statistics show the change in lifestyles and responsibilities of aging (老齡化) Americans. The average middle-aged couple can look forward to caring for elderly parents sometime after their own children have grown up. Moreover, because people today live longer after an illness than people did years ago, family members must provide long-term care. These facts also mean that after caregivers provide for their elderly parents, who will eventually die, they will be old and may require care too. When they do, their spouses (配偶) will probably take care of them because they have had fewer children than their parents did.

Because Americans are living longer than ever, more social workers have begun to study ways of caregiving to improve the care of the elderly. They have found that all caregivers share a common characteristic; They believe that they are the best people for the job. The social workers have also discovered three basic reasons why the caregivers take on the responsibility of caring for an elderly, dependent relative. Many caregivers believe they had an obligation (職責) to help their relatives. Some think that helping others makes them feel more useful. Others hope that by helping someone now, they will deserve care when they become old and dependent.

Samuel Preston's study shows that______.

A．lifestyles and responsibilities of the elderly are not changing

B．most American couples over 40 have no living parents

C．middle-aged Americans have to take care of their children and parents at the same time

D．elderly people may need care for a long time because they live longer after an illness