Leukaemia is cancer of blood-forming cells. Leukaemia usually causes large numbers of white blood cells to be made. These abnormal cells usually can't carry out the normal functions of white blood cells. They crowd the bone marrow and spill into the blood and may then spread into organs such as the liver, spleen, lungs and kidneys. Sometimes, they may also spread into the fluid around the brain and spinal cord. Because there are so many abnormal white cells crowded into the bone marrow, the marrow sometimes can't make enough normal red blood cells, white blood cells and platelets. Thus, option B is correct.