Conclusion: People should throw away their toothbrushes after only four weeks of use.
Reasoning: In that time, enough bacteria has accumulated to cause strep throat and pneumonia.
To WEAKEN this argument we will need an answer choice that suggests we should not dispose of our 4-week old toothbrushes.
It seems that debate here is between (C) and (E), so I will focus on these two answer choices.(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.
Contaminated toothbrushes, i.e. those brushes with bacteria, are no more likely to cause strep throat than non-contaminated toothbrushes. Therefore, one should not throw away their 4-week old toothbrushes. ANSWER.
(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.
Let's say I have a contaminated 4-week old toothbrush, on which a small colony bacteria has grown. If I do not throw the toothbrush away, I am likely to get strep throat. Nevertheless, I continue using the toothbrush for another two weeks. Now at week 6 the colony of bacteria is still there. According to answer (E) the colony has not grown (greater length of use of a toothbrush did not correlate...
Of course I should still throw the toothbrush away because it is contaminated. Remember, we have to find an answer choice that suggests that it makes no sense throwing our toothbrush away. (E) however suggests that we should still throw the toothbrush away at week 6, regardless of whether it is less contaminated than it was at week 4.
Magoosh Test Prep