<prompt> Site of RBC formation in 20-year-old healthy male isFlat bonesLong bonesLiverYolk sac  <response>: RBC formation in 20-year-old healthy adult takes place in flat bones. It also occurs in end of long bones.RBC formation during mesoblastic stage 3rd week to 3rd month of intrauterine life takes place in yolk sac.RBC formation during hepatic stage after 3 months of intrauterine life takes place in liver.Ref: Medical physiology for UG students, Indu Khurana, pg 104 