问题:
[单选题]
根据下列短文,回答{TSE}题。 Despite the fact that today viruses(病毒)are known to cause cancer in animals and incertain plants,there exists a great reluctance to accept viruses as being of importance in humancanc
A viruses are known to cause cancer in animalsB at present,human cancer is not believed to be contagious(传染的)C there are many known causes for the transformation of a normal cell to a cancer cellD results of experiments on plants and animals do not vary greatly from species to species