A、Damaging organs made from the cells. B、Causing disability. C、Damaging the Yamanaka factors in human body. D、Causing heart atta

An end to grey hair and crows-feet could be just 10 years away after scientists showed it is possible to reverse ageing in animals.
    Using a new technique which takes adult cells back to their embryonic form, US researchers at the Salk Institute in California, showed it was possible to reverse ageing in mice, allowing the animals to not only look younger, but live for 30％ longer.
    The technique involves stimulating four genes which are particularly active during development in the womb. It was also found to work to turn the clock back on human skin cells in the lab, making them look and behave younger.
    Scientists hope to eventually create a drug which can mimic the effect of the found genes which could be taken to slow down, and even reverse the ageing process. They say it will take around 10 years to get to human trials.
    "Obviously, mice are not humans and we know it will be much more complex to rejuvenate a person. But this study shows that ageing is a very dynamic and plastic process, " said Dr. Juan Carlos Izpisua Belmonte, a professor in Salk’s Gene Expression Laboratory.
    Scientists have known for some time that the four genes, which are known collectively as the Yamanaka factors, could turn adult cells back to their stem cell state, where they can grow into any part of the body. But it was always feared that allowing that to happen could damage organs made from the cells, and even trigger cancer.
    However, it was discovered that stimulating the genes intermittently reversed ageing, without causing any damaging side effects.
    In mice with a premature ageing disease, the treatment countered signs of ageing and increased their lifespan by 30％. If it worked similarly in humans it could allow people to live until more than 100 years old. In healthy mice it also helped damaged organs to heal faster.
    Questions 23 to 25 are based on the recording you have just heard.
    23. What did the research carried out by US researchers at the Salk Institute in California show?
    24. What can we know about the new technique?
    25. What is the potential risk of turning adult cells back to their stem cell state?