2043. What character can be added to both of these characters to give other characters? 火_ -> _欠

火  KA, hi - fire

欠  KETSU, ka(ku), ka(keru) - lack

Add 火:火+火 火+欠  

火  KA, hi - fire

炎  EN, honou - flame

炊  SUI, ta(ku) - burn, light a fire, boil, cook