Correct Option: D

Haematopoiesisis the formation of blood cellular components. The sites where haematopoiesis occurs change during embryonic development, but in adult mammals, the bone marrow is the major site of haematopoiesis. Haematopoietic stem cells in the bone marrow reside in a specialised microenvironment known as the hematopoietic stem cell niche, composed of osteoblasts, mesenchymal cells and sinusoidal vessels.