请教大家一道题

17.(Z)The ancient Nubians inhabited an area in which typhus occurs, yet surprisingly few of their skeletons show the usual evidence of this disease.  The skeletons do show deposits of tetracycline, an antibiotic produced by a bacterium common in Nubian soil.  This bacterium can flourish on the dried grain used for making two staples of the Nubian diet, beer and bread.  Thus, tetracycline in their food probably explains the low incidence of typhus among ancient Nubians.

Which of the following is an assumption on which the argument relies?

A.   Infectious diseases other than typhus to which the ancient Nubians were exposed are unaffected by tetracycline.

B.   Tetracycline is not rendered ineffective as an antibiotic by exposure to the processes involved in making bread and beer.

C.   Typhus cannot be transmitted by ingesting bread or beer contaminated with the infectious agents of this disease.

D.  Bread and beer were the only items in the diet of the ancient Nubians which could have contained tetracycline.

E.   Typhus is generally fatal.

C为什么不对
        如果C成立不就是说明Typhus是发生过的啊

原文大意——

因为——吃了抗体

所以——百毒不侵

本题的关键是要找出抗体和病毒之间的关系，以证明结论的正确。所以，B最合适。

C的条件如果成立，则是出现了另一种造成百毒不侵的原因，而忽略了抗体的因素。因此，也就不是前提条件和结论之间的桥梁。