Prolonging human life has increased the size of the human population. Many people alive today would have died of childhood diseases if they had been born 100 years ago. Because more people live longer, there are more people around at any given time. In fact, it is a decrease in death rates, not an increase in birthrates, that has led to the population explosion.
Prolonging human life has also increased the dependency load. In all societies, people who are disabled or too young or too old to work are dependent on the rest of society to provide for them. In hunting and gathering cultures, old people who could not keep up might be left behind to die. In times of famine (饥荒), infants might be allowed to die because they could not survive if their parents starved, where as if the parents survived they could have another child. In most contemporary societies, people feel a moral obligation (责任) to keep people alive whether they can work or not. We have a great many people today who live past the age at which they want to work or are able to work; we also have rules which require people to retire at a certain age. Unless these people were able to save money for their retirement, somebody else must support them. In the United States many retired people live on social security checks which are so little that they must live in near poverty. Older people have more illnesses than young or middle-aged people; unless they have wealth or private or government insurance, they must often “go on welfare” if they have a serious illness.
When older people become senile (衰老的) or too weak and ill to care for themselves, they create grave problems for their families. In the past and in some traditional cultures, they would be cared for at home until they died. Today, with most members of a household working or in school, there is often no one at home who can care for a sick or weak person. To meet this need, a great many nursing homes and convalescent (疗养的) hospitals have been built. These are often profit making organizations, although some are sponsored by religious and other nonprofit groups. While a few of these institutions are good, most of them are simply “dumping (倒垃圾的) grounds” for the dying in which “care” is given by poorly paid, overworked, and under skilled personnel (员工).
The author believes that the increased size of the human population results from _______.

A．an increase in birthrates	B．the industrial development
C．a decrease in death rates	D．childhood diseases

It can be inferred from the passage that in hunting and gathering cultures _______.

A．it was a moral responsibility for the families to keep alive the aged people who could not work

B．the survival of infants was less important than that of their parents in times of starvation

C．old people were given the task of imparting (传授) the cultural wisdom of the tribe to new generations

D．death was celebrated as a time of rejoicing for an individual freed of (免除) the hardships of life

The phrase “this need” in the last paragraph refers to ________.

A．prolonging the dying old people’s lives

B．reducing the problems caused by the retired people

C．making profits through caring for the sick or weak people

D．taking care of the sick or weak people

According to the passage, which of the following statements about the old people in the United States is true?

A．Many of them live on social security money which is hardly enough.

B．Minority of them remain in a state of near poverty after their retirement.

C．Many nursing homes are sponsored by religious and nonprofit groups.

D．Older people have wealth or private insurance if they have a serious illness.