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.
Type - weaken
Boil it down - Contamination of toothbrushes occur after four weeks of usage and hence people should replace their toothbrushes once a month.
Pre-thinking - to weaken this we need an option that tells that probability that people will contract pneumonia and strep throat is minimal even after first four weeks
(A) The dental researchers could not discover why toothbrush contamination usually occurred only after toothbrushes had been used for four weeks. - Irrelevant - reason is not important
(B) The dental researchers failed to investigate contamination of toothbrushes by viruses, yeasts, and other pathogenic microorganisms. - Out of scope
(C) The dental researchers found that among people who used toothbrushes contaminated with bacteria that cause pneumonia and strep throat, the incidence of these diseases was no higher than among people who used uncontaminated toothbrushes. - Correct - If this is true then there is no point replacing the toothbrush every 4 weeks
(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. -Irrelevant
(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. - Incorrect - what about the period of time from 4 weeks to 6 weeks .
Answer C
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