Even if we have an extremely healthy diet and lifestyle, the human body is programmed to wear out at a maximum of about 120 years, and usually less. We all have a biological clock inside us which determines the moment when our organs cease to function properly. This is because our cells have stopped renewing themselves and our body can no longer repair itself. This is also the moment when we are more likely to begin to suffer from the diseases of old age such as arthritis and Alzheimer’s. However, rapid advances in DNA research are beginning to throw light on the secrets of the ageing process. By the end of this century we could literally have the power of life over death.
Although it has long been accepted that humans have a fixed lifespan, it is also a fact that certain other organisms, such as reptiles and amphibians, appear to live indefinitely. The only reason we do not see 500-year-old alligators is because in the wild their lives are always in danger, from man, from pollution and from other animals. When they are kept in zoos they do not seem to age at all after they are fully grown. The same is true of some species of fish, which grow indefinitely and show no signs of ageing. The existence of animals with no fixed lifespan seems to indicate that an age gene really does exist. It is this gene which scientists are searching for, which may delay or repair damage to the body caused by ageing.
Another new area of research involves the oxidation（氧化） theory, which says that ageing is caused by the same process that makes iron rust. In controlled experiments, the lifespans of certain animals were shown to be lengthened with anti-oxidants; for example, the lifespan of mice can be increased by 30%. Antioxidants are already being used in face creams and other cosmetics, and they are likely to play an important part in keeping people physically young.
Perhaps the most immediate advance we are likely to see in the battle to halt（停止）the ageing process will be organ replacement. By the year 2020 it is likely that we will be replacing injured bones or even organs like livers and kidneys with ones “grown” in laboratories. By 2050 perhaps every organ in the body, except the brain, will have become commercially available. Recent experiments also show that it may one day be possible to “grow” new organs inside our body to replace worn-out ones, something which lizards and alligators already do.
Suddenly immortality（不死，不朽） seems within reach. We can begin to imagine a future where we are born, we grow to maturity, but we never grow old and die. But do we really want to live forever?
When all humans reach a certain age,         .

A．they suffer the effects of their diet and lifestyle

B．the organs stop to perform appropriately

C．their cells continue to renew themselves

D．they develop arthritis and Alzheimer’s

The purpose of showing the case of alligators is to prove         .

A．alligators are in danger in the wild because of the threat from man, pollution and other animals

B．it is widely accepted that humans have a fixed lifespan

C．there exists an age gene which may control ageing

D．the age gene damages the body

The underlined phrase “live indefinitely” in Paragraph 2 probably mean         .

A．live for a period of time without a fixed end

B．live without a clear aim

C．live in an uncertain way

D．live without being fully grown

It can be inferred from Paragraph 4 that         .

A．by 2050 we might have most of our worn-out organs replaced with new ones commercially

B．never can the ageing process be avoided

C．livers and kidneys are sure to be grown in laboratories by the year 2020

D．lizards and alligators grow new organs inside their body to replace worn-out ones

What is the main topic of this passage?

A．DNA researches show how our cells renew themselves.

B．Anti-oxidants are likely to play an important part in keeping people young.

C．How our biological clock works?

D．Eternal（永恒的） youth: new developments in anti-ageing research.

By saying “But do we really want to live forever”, the author may probably mean         .

A．a future where we are born, we grow to maturity, but we never grow old and die is on its way

B．he is uncertain whether we can live forever

C．it remains to be seen whether immortality is a blessing or a curse

D．immortality is no longer a dream