It's definitely letter A. Mononucleosis
Supplements do not prevent a cold or the flu. It is a common misconception that Vitamin C can prevent sickness when is reality there is not evidence to support that claim.
The answer to this statement is true.
It would be true for most hiv if the person lacks ccr5 on the cells surface. but people with two copies of the ccr5-delta32 gene are basically immune to hiv infection.