CR # 1

Dental researchers recently discovered that toothbrushes

can become contaminated with bacteria 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

bacteria 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 bacteria being present