Hematopoiesis in prenatal stages occurs in

The correct option is A Yolk sac
Haematopoiesis refers to the process of the formation of mature blood cells from the immature myeloid progenitor cells. In the prenatal stage, it occurs in the yolk sac. Gradually, as the development proceeds, it occurs in the liver and then the bone marrow. In adults, it occurs in bone marrow and lymphatic tissues.

Hence, the correct answer is 'Yolk sac'.