Chronic Fatigue Syndrome (CFS) Is a Debilitating Disease of Unknown

Chronic fatigue syndrome (CFS) is a debilitating disease of unknown etiology that is estimated to affect 17 million people worldwide. Studying peripheral blood mononuclear cells from patients with CFS, researchers identified DNA from a human gamma-retrovirus (XMRV) in 68 of 101 patients, compared with 8 of 218 healthy controls.
What percent of the healthy controls were found to have XMRV DNA?

A) 3.7%
B) 21.3%
C) 23.8%
D) 67.3%