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  3. Despite the fact that today virus are known to cause cancer in animals and in plants, there exists a great reluctance to accept

Despite the fact that today virus are known to cause cancer in animals and in plants, there exists a great reluctance to accept

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问题     Despite the fact that today virus are known to cause cancer in animals and in 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 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 of the cell of origin. The transformation of a normal cell into a cancer cell may have more than one kind of cause, but there 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 infectious, many persons believe that because viruses are infectious agents they cannot possibly be of importance in human cancer. However, viruses can mutate 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 latent 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 agents of most, if not all cancer, including cancer in man.
What is the passage mainly about?
选项 A、Viruses are the causative agents of most cancer.
B、How and why viruses mutate.
C、Basic biological phenomena in plants, animals and man.
D、Why the human cancer is not infectious.
答案A
解析 文章开头部分说病毒是导致动植物癌症的主要原因，后文又继续补充它也是人类癌症的重要原因。由此可知，病毒是大多数癌症的病原体。据此判断，本题选A。
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