93. Dental researchers recently discovered that tooth-brushes can become contaminated with bacterial that cause pneumonia and strep throat. They found that contamination usually occurs after toothbrushes have been used for four weeks. For that reason, people should replace their toothbrushes at least once a month.

 Which of the following, if true, would most weaken the conclusion above?

(A) The dental researchers could not discover why toothbrush contamination usually occurred only after toothbrushes had been used for four weeks.

(B) The dental researchers failed to investigate contamination of toothbrushes by viruses, yeasts, and other pathogenic microorganisms.

(C) The dental researchers found that among people who used toothbrushes contaminated with bacterial that cause pneumonia and strep throat, the incidence of these diseases was no higher than among people who used uncontaminated toothbrushes.

答案是C没有问题. 但OG对A的解释我看不明白" The recommendation to change every four weeks is not weakened simply because researcher cannot explain why it takes that long for contamination to occur"

我想的A无关就是污染的原因和生病与污染无关,谁能帮我理解理解?

E选项为什么不对？

(E)The dental researchers found that, after six weeks of use,greater length of use of a toothbrush did not correlate with a higher number of bacteria being present.

OG的解释我看不懂，E说6个月都和细菌没关系，那四个月不就更没关系了吗？不正好削弱了结论了？

楼上的对E的理解有偏差,

E是说:6个月以后,细菌数量不再增加了.

套公式吧：

因：使用4周以上的牙刷通常会受到细菌污染。

果：至少一个月换一次牙刷。

要求weaken

因是调查结果算是有因，果是推测，所以应当是有因无果：虽然牙刷使用四周以上会被细菌污染，但是不用至少一个月换一次牙刷，即牙刷感染不等于牙齿感染