For years, doctors have been trying to find

[Vincen]

For years, doctors have been trying to find a cause for Chronic Fatigue Syndrome (CFS). The devastating illness tends to strike healthy and fairly active individuals with no other history of medical problems or conditions. Recently, doctors in California have found that over 70% of those individuals diagnosed with CFS are infected with a rare enterovirus that is almost never found in the healthy population. As a result, they believe that this enterovirus is the primary cause of many cases of CFS.

Which if the following is an assumption upon which the doctors' theory depends?

A) There are not other viruses that may cause Chronic Fatigue Syndrome.
B) The rare enterovirus was present at the onset of these patients' Chronic Fatigue Syndrome.
C) The laboratory technicians analyzing the presence of the enterovirus in the patients' blood and tissues did not make some mistakes in their analysis.
D) The severity of the symptoms among the patients diagnosed with CFS does not vary widely.
E) The rare enterovirus is commonly seen in patients that are severely ill.

The OA is B.

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