Despite the fact that today viruses are known to cause cancer in animals and in certain plants, where exists a great reluctance 【M1】______ to accept viruses as been of importance in human cancer. Basic 【M2】______ biological phenomena generally does not differ strikingly as 【M3】______ one goes from one species to other. It should be recognized that 【M4】______ 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 with apparent restraint. 【M5】______ Cancer cells 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 to a cancer cell may 【M6】______ have more than one kind of cause, but theres good reason to consider the relationships exist between viruses and cancer. Since theres no evidence which human cancer, as generally 【M7】______ experienced, is infectious, many person believe that because 【M8】______ viruses are infectious agents, they can possibly be of important in 【M9】______ human cancer. Furthermore, viruses and examples are known in which a virus never kills its host can mutate to form. a new strain 【M10】______ 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.
【M1】