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  3. Two recent studies have confirmed the belief that size does matter, at least when it comes to cancer. The first builds on previo

Two recent studies have confirmed the belief that size does matter, at least when it comes to cancer. The first builds on previo

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问题     Two recent studies have confirmed the belief that size does matter, at least when it comes to cancer. The first builds on previous evidence that being overweight is a major risk factor for breast cancer, and the second suggests that tall people are prone to a number of common cancers.
    Our bodies contain trillions of cells that are constantly renewing or repairing themselves. Normal cells know where they are in the body, and behave appropriately. They grow and reproduce only when required, and self-destruct when they come to the end of their life. But, because of the problems in their software(DNA), cancer cells no longer respond to these normal signals and grow out of control.
    Numerous mistakes are made during cell division every minute of every day and the body has natural defense systems to spot the damage and repair it, or kill the affected cells. The more cells you have, and the longer you live, the greater the odds of one of these mistakes slipping through. And that is without the external influence of carcinogens(诱癌因素).
    Risk factors such as being overweight or taller than average are not direct carcinogens and it is often unclear why they increase the risk of cancer. The link with height may simply be down to taller people having more cells, meaning that there is more opportunity for things to go wrong. The link with obesity is likely to be more complex, but in the case of breast cancer it is thought that overweight women tend to produce more oestrogen(雌激素), a hormone(荷尔蒙)that can act as a "fertilizer" for some types of breast cancer.
    Whatever the cause, the result is the same. Once enough mistakes have occurred for a cell to escape the body’s normal control mechanisms, it divides unchecked and a tumor(肿瘤)develops.
    Will we have a cure? Probably not. But recent advances using drugs that target proteins in cancer cells to control their growth and spread suggest that we are about to enter an era when we may be able to slow and control cancer to such an extent that it will become a chronic(慢性的)disease that can be held in check.
What does the author say about normal cells in our body?
选项 A、They will kill other cells when coming to the end of life.
B、They can not be renewed once they have been destroyed.
C、They grow and destroy themselves according to the need of the body.
D、They can only be repaired and reproduced by other factors.
答案C
解析 根据题干关键词normal cells定位到第二段第二、三句：Normal cells know where they are in the body，and behave appropriately．They grow and reproduce only when required，and self-destruct when they come to theend of their life．正常的细胞知道自己在身体里的位置，行为恰当。他们只有需要时才成长，而生命结束时就自我毁灭。C)项是原文的同义转述，故为答案。
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