求助 dental research

choclee

Dental researchers recently discovered that tooth-brushes can become contaminated wth 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.


(D) The dental researchers found that people who rinsed their toothbrushes thoroughly in hot water after each use were as likely to have contaminated toothbrushes as were people who only rinsed their toothbrushes hurriedly in cold water after each use.


(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 bacterial being present. C

E为什么不对？
Dental researchers recently discovered that tooth-brushes can become contaminated wth 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.
Not knowing why doesn't attack the basis for the conclusion. It just means it happens, but we don't know why. No reason to think they're wrong.
(B) The dental researchers failed to investigate contamination of toothbrushes by viruses, yeasts, and other pathogenic microorganisms.
Out of scope. It doesn't matter that they failed to investigate other contamination, the focus is on the contamination they DID find.
(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.
This is a close one, but in the end incorrect. The premise of the stem is all about the length of time the person uses the toothbrush. That is not mentioned at all here. It does weaken, but E weakens more because it undercuts the basic reason for the stem's conclusion.
(D) The dental researchers found that people who rinsed their toothbrushes thoroughly in hot water after each use were as likely to have contaminated toothbrushes as were people who only rinsed their toothbrushes hurriedly in cold water after each use.
Out of Scope. This has nothing to do the length of time the toothbrush is used. This has to do with a variable that changes from person to person. The length of use has to do with every toothbrush user. This doesn't weaken the stem.
(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 bacterial being present.
This undercuts the premise of the stem by saying that after 6 weeks of use, there is no difference between toothbrushes. Sure their correlation worked after 4 weeks, but any variation was completely gone within 2 more weeks and their conclusion that we should toss the toothbrush after 4 weeks is invalid because it doesn't hold true after 6 weeks.

gar_bbbbb

因为题目说的是一个月，就是四周，而E选项讨论的是六周，我觉得out of scope。