The researchers' hypothesis is based on which of the following assumptions? A. Delta-32 does not prevent a carrier from contracting any disease other than the plague. B. The plague is not similar to other diseases caused by bacteria. C. Delta-32 did not exist in its current form until the sixteenth century. D. No one who tested positive for Delta-32 has ever contracted a disease caused by bacteria. E. The plague does not cause genetic mutations such as Delta-32.