Healthy lungs produce a natural antibiotic that protects them from infection by routinely killing harmful bacteria on airway surfaces. People with cystic fibrosis, however, are unable to fight off such bacteria, even though their lungs produce normal amounts of the antibiotic. The fluid on airway 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?
A. When the salt concentration of the fluid on the airway surfaces of healthy people is raised artificially, the salt concentration soon returns to normal.
B. A sample of the antibiotic was capable of killing bacteria in an environment with an unusually low concentration of salt.
C. When lung tissue from people with cystic fibrosis is maintained in a solution with a normal salt concentration, the tissue can resist bacteria.
D. Many lung infections can be treated by applying synthetic antibiotics to the airway surfaces.
E. High salt concentrations have an antibiotic effect in many circumstances.
我选B啊，因为只有在盐分低的环境下antibiotic才能起作用，正好在high salt concentration
和antibiotic ineffective之间搭了桥
可是正确答案是C，为什么，为什么啊？？？？？？？
NN指教，帮忙啊！！！！！！！谢谢谢谢！！！！！！！！！！！！
B并不能说明antibiotic不能在high salt concentration下失效。而C说将病人的肺部的盐的浓度降下来后，这些组织就能抵抗细菌了。这是通过非B推出非A来证明A能推出B。
推理链： High salt environmentsðð antibiotic becomes ineffective
D选项：Normal saltà
（people with CF are unable to fight off harmful bacteria）à antibiotic becomes ineffective
无因也有果，标准的消弱。
推理链： High salt environmentsðð antibiotic becomes ineffective
D选项：Normal saltà
（people with CF are unable to fight off harmful bacteria）à antibiotic becomes ineffective
无因也有果，标准的消弱。
明白无因有果的意思了
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