<prompt> Fatty acids are the main source of energy for :MusclesHeartLiverRBC  <response>: Fed State Preferred fuelStarvation preferred fuelRBCHeartBrainLiverMuscleAdipose tissueGlucoseFatty acidsGlucoseGlucoseGlucoseGlucoseGlucose Ketone bodiesKetone bodiesFatty acids proteinsFatty acidsFatty acids 