GWD5---26 求教

yvonne19831204

Q26:

Healthy lungs produce a natural antibiotic that protects them from infection by routinely killing harmful bacteria on airway surfaces.  eople with cystic fibrosis, however, are unable to fight off such bacteria, even though their lungs produce normal amounts of the antibiotic.  The fluid on a0.irway surfaces in the lungs of people with cystic fibrosis has an abnormally high salt concentration; accordingly, scientists hypothesize that the high salt concentration is what makes the antibiotic ineffective.

Which of the following, if true, most strongly supports the scientists’ hypothesis?

When the salt concentration of the fluid on the airway surfaces of healthy people is raised artificially, the salt concentration soon returns to normal.

A sample of the antibiotic was capable of killing bacteria in an environment with an unusually low concentration of salt.

When lung tissue from people with cystic fibrosis is maintained in a solution with a normal salt concentration, the tissue can resist bacteria.

Many lung infections can be treated by applying synthetic antibiotics to the airway surfaces.

High salt concentrations have an antibiotic effect in many circumstances.

为什么不能选B, 答案是C

lawyer_1

结论为：高盐度（因）使抗体无效（果）。B的意思为：低盐度下抗体有效（别的因/无果）。 C的意思为：正常盐度下抗体有效（无因/无果）。

[此贴子已经被作者于2005-12-30 23:36:52编辑过]

lawyer_1

这道题的B有点讨厌，所以再补充点

原文的现象：正常时（盐度也正常，注意正常的盐度不意味着盐度有多少，高也好，低也罢，只要是正常），抗体能杀菌。盐度高时，不能杀菌

结论：盐度高是这种不能杀菌现象的因。

什麽是无因,就是将原因去掉，那麽原因（高盐度）去掉后就变成了正常。如果是盐度低，变成了另一个原因（低盐度）。而另外一个原因和原文无关。在这意义B不是答案。

双鱼游

O(∩_∩)O谢谢lawyer