The correct option is A Femur
The bone marrow is the location where all cells of the immune system begin their development from primitive stem cells. Bone marrow is also a key component of the lymphatic system, producing the lymphocytes that support the body's immune system. Red marrow is found mainly in the flat bones, such as the pelvis, sternum, cranium, ribs, vertebrae and scapulae, and in the cancellous material at the epiphyseal ends of long bones such as the femur and humerus.