i think why sweat is the answer even though it is also considered infectious its because you have to actually select the least infectious one. Or the one which has a low record of spreading the infection. charz
that is to prevent the spread of infection to the other person (when we sneeze or cough we tend/ unintentionally use our hand to cover it), so hand washing is the answer ^^
i think the answer is B because we should not let someone with colds in a facilty with old people inside. they get sick easy. handwashing cant stop sneezing and runny nose.