题目内容：

Since the beginning of history, man has been attracted by the idea of living forever, of winning the fight against death and disease. So far, this has only remained a dream. Many people have wondered whether it would be possible to find a way to preserve human bodies, and what would be the best way.

It has long been known that meat of fruit can be kept fresh for long periods by freezing; in ancient China, for example, food was stored with ice to keep it fresh. This method could also be useful for preserving humans.

However, most living beings that exist under warm conditions die when frozen. This is because of the harmful effects of freezing ice crystals(晶体), which not only are larger than the volume(体积) of the water originally in the cells, but also form sharp cutting shapes that harm the cells.

In the 1940s Dr B.J. Luyet and a group of scientists in England were working on the problem of freezing cells without damaging them. Since the harm caused by ice crystals was the main cause of damage, Luyet suggested removing some or all of the water from the cells before freezing them.

Using living cells form chicken, Luyet and his assistants discovered that they could partly dry the chicken cells, using a mixture of the white part of an egg and glycerin (丙三醇). Some success was obtained. The chicken cells were dried, frozen for a period of time, and then carefully unfrozen. Almost all the cells recovered when they reached normal temperatures.

Since then, the cooling of whole animals to a temperature far below freezing point for later unfreezing has become more of a possibility, and the glycerin method would probably be used to accomplish this. When this can be done completely and successfully, science will have moved much closer to its aim of freezing and storing incurable patients until the day they can be cured.

1.What does the passage mainly talk about?

A．Easy but practical ways to remove water from living cells.

B．The possibility of preserving human bodies by freezing.

C．The practice of preserving food by freezing.

D．The harmful effects of freezing.

2.The idea of freezing human bodies to preserve them ______________.

A．has already been realized

B．was invented in ancient China

C．has its roots in the way of storing food

D．is widely accepted by the scientific world

3.According to the text, freezing _________________.

A．is harmful to living cells

B．is the best way of preserving food

C．reduces the volume of water in living cells

D．is a way of removing water from living cells

4.What can be inferred from the last paragraph?

A．It is impossible to have whole animals frozen.

B．It remains unknown how to unfreeze frozen animals.

C．Freezing incurable patients for later treatment is still an idea.

D．The glycerin method has already been adopted to treat patients.