单选题
Passage 4
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.
单选题
According to the passage, which is NOT true?
【正确答案】
D
【答案解析】[解析] 根据文章第一段第一句“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．”可知，尽管人们都知道病毒可以在动物和植物中引发癌症，却仍不愿意相信 病毒对于人类癌症也有着十分重要的作用。由此判断，A、B两项正确；根据文章第一段第 二句“Basic biological phenomena generally do not differ strikingly as one goes from one species to another．”可知常见的生物现象一般不能鲜明地区分病毒从一种物种转移到另一种物种。所 以C正确；D项说癌症可由某些特定细胞转化而来。根据文章第一段倒数第二句“Cancermay originate in many different kinds of cell，but the cancer cell usually continues to carry certain traits ofthe cell oforigin．”可知，癌症可能由许多种不同的细胞引发，但是癌细胞通常会继续携带 原始细胞的某些痕迹。所以D项不正确。据此判断，本题选D。
单选题
According to the passage, which is true?
【正确答案】
C
【答案解析】[解析] 根据文章第二段第二句“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．”可 知，病毒是可以变异的，一个不能导致受体死亡的病毒会变异成一种新式病毒，这种病毒常 常会导致受体的死亡。所以C正确。据此判断，本题选C。
单选题
It is possible that viruses cause human cancer because______
【正确答案】
D
【答案解析】[解析] 根据文章最后一段倒数第二句“It does not seem unreasonable to assume that an innocuous latent virus might mutate to form a strain that causes cancer．”可知，我们有理由假设 一个不具危害性的潜在病毒可能会变异成另一种能够引发癌症的新型病毒。据此判断，本 题选D。