This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Haematology, Subject name: Pathology
Common site of haematopoiesis in fetus is - 
Select and explain. 
A. Liver, B. Spleen, C. Bone marrow, D. Gut
A: Liver
Answer: A: Liver 
Explanation: Blood cell progenitors first appeared during the third week of embryonic development in yolksac.But its contribution is only transient. During 3rd month of embryogenesis hematopoetic stem cells migrate to liver which becomes the chief site of blood cell formation until sholy before bih. Reference :Robbins and Cotran Pathologic basis of disease.South Asia Edition-9 volume 1.page no. 414