The correct answers would be:
A. Cold - handwashing
Washing of your hands helps to prevent you in contracting and spreading of germs such as the cold virus. Hand washing kills off the nasty bacteria.
B. AIDS - Avoidance of IV drugs.
One method of contracting AIDS is through IV drugs. People that take IV drugs can share needles that have come into contact with contaminated blood. Do not share needles or take IV drugs and you reduce your risk of contracting AIDS.
C. Measles - Vaccination
Having the measles vaccination as a child prevents you from contracting the virus.