Correct answer is c - Blood cell are produced in the skeletal system.
Red blood cells are produced on a regular basis in the bone marrow. Bone marrow is a red spongy material found within the cavities of many of the large bones of the body.
Red blood cell start as immature cell in the bone marrow and after about seven days of maturation, they are released into the bloodstream, that is, the circulatory system where they circulate for about 120 days before being replaced with new ones.