3. 咖啡因(Caffeine)分子內之各種原子質量占比分別為C = 49.48%,H = 5.15%,N = 28.87%,O = 16.49%。已知咖啡因之分子量為194.2,請推測其分子式,下列何者正確?(A) C4H5N2O (B)