As richard himself to a fourth beer, he announced to everyone at the barbecue that alcohol is healthy in moderation. how does the text define "moderation"

The answer is "two drinks per day, no more than two drinks of moderate size per day".

Moderation refers to a way that is sensible and not intemperate. Eating food with some moderation is a vital component to keeping up a sound eating regimen. That implies you have a tad of everything, as opposed to pigging out, say, on steak and frozen yogurt. 

The answer is price.