The use of Antibiotics, as Virus's are not affected by them.
Answer - A. Depressants
Reasoning - Why his Lungs, Kidney, Liver are failing is because of depressants. When taking depressants and overdosing like cough syrup can cause the organs go into a state of depressant. Which causes the organs to have problems and can kill him.
I believe you answer is they both transmission signals through radio waves.