CR, Difficulty level: 700, Logical flaw, Source: Kaplan

[aishwaryav12]

Mary Mallon, known as "Typhoid Mary," was a typhoid "carrier" who was infected with the typhoid bacillus for a prolonged period of time. She developed neither typhoid fever nor its symptoms; however, other people could, and did, develop this disease after contact with her.

Which of the following is best supported by the statements above?

A. Typhoid fever is not always fatal.

B. Typhoid fever is equally communicable whether the person infected with the typhoid bacillus actually has the disease or not.

C. The absence of the usual symptoms of typhoid fever is not always a reliable indicator that one does not have typhoid fever.

D. Typhoid fever sometimes occurs even when the typhoid bacillus is not present.

E. The typhoid bacillus does not always cause typhoid fever.

[nonplus2]

It is a MUST BE TRUE question

A. Typhoid fever is not always fatal. - We can't infer this. Maybe, Mary had very high immunity.
B. Typhoid fever is equally communicable whether the person infected with the typhoid bacillus actually has the disease or not. 'equally communicable' is the part to look for. We can't say from the mentioned text that people both who are infected and who are not infected have equal capacity to transmit the disease.
C. The absence of the usual symptoms of typhoid fever is not always a reliable indicator that one does not have typhoid fever. We can't say for sure just after observing this particular case.
D. Typhoid fever sometimes occurs even when the typhoid bacillus is not present. typhoid bacillus may not cause typhoid fever, but we can't say for sure that fever might occur even when bacillus is not present.
E. The typhoid bacillus does not always cause typhoid fever. Correct Answer. This is the generalization(a correct one) derived from this particular case.