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  3. Despite the fact that today viruses (病毒) are known to cause cancer in animals and in certain plants, there exists a great reluct

Despite the fact that today viruses (病毒) are known to cause cancer in animals and in certain plants, there exists a great reluct

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问题     Despite the fact that today viruses (病毒) are known to cause cancer in animals and in certain plants, there exists a great reluctance to accept viruses as being of importance in human cancer. Basic biological phenomena generally do not differ strikingly as one goes from one species to another. It should be recognized that cancer is a biological problem and not a problem that is unique for man. Cancer originates when a normal cell suddenly becomes a cancer cell which multiplies widely and without apparent restraint. Cancer may originate in many different kinds of cell, but the cancer cell usually continues to carry certain traits (特性) of the cell of origin. The transformation of a normal cell into a cancer cell may have more than one kind of cause, but them is good reason to consider the relationships that exist between viruses and cancer.
    Since there is no evidence that human cancer, as generally experienced, is infections, many persons believe that because viruses are infections agents they cannot possibly be of importance in human cancer. However, viruses can mutate (突变) and examples are known in which a virus that never kills its host can mutate to form a new strain of virus that always kills its host. It does not seem unreasonable to assume that an innocuous (无害的) latent (潜伏的) virus might mutate to form a strain that causes cancer. Certainly the experimental evidence now available is consistent with the idea that viruses as we know them today, could be the causative (引起……的) agents of most, if not all cancer, including cancer in man.  
The possibility that a virus causes human cancer is indicated by ______.
选项 A、the fact that viruses have been known to mutate
B、the fact that a cancer-immune individual may lose his immunity
C、the fact that production of human cancer cells might be due to a genetic factor
D、the fact that man is host to many viruses
答案A
解析
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