Notice how I said person B, A, C,? Blood Alcohol content! Person A could have died from purely natural causes or from passing out from drinking in the kitchen and choking on their own vomit! Eeeew! Or A could have died from old age, disease, starvation (it's a very sparse kitchen) radiation, or maybe they accidentally locked themselves in one of those old-old-style refrigerators without the little magnetic sealing strip!