What are the two main divisions of the human skeleton?

Rationale:
A. Cranial and Caudal refers to directional terms in anatomy (head and tail ends), not divisions of the skeleton.
B. Left and Right simply describe sides of the body and do not represent structural divisions of the skeletal system.
C. The axial skeleton includes the skull, vertebral column, and thoracic cage (ribs and sternum) and serves primarily to protect vital organs and provide structural support. The appendicular skeleton includes the upper and lower limbs, shoulder girdle, and pelvic girdle, which facilitate movement and interaction with the environment. These two divisions together provide a framework for the body, support posture, and enable locomotion.
D. Upper and lower are general terms for parts of the body and do not accurately describe the anatomical divisions of the skeleton.

Rationale:
A. Osteoblasts are specialized bone-forming cells responsible for producing new bone tissue. They secrete collagen and other components of the bone matrix and play a vital role in bone growth, repair, and remodeling. Once trapped in the matrix they secrete, osteoblasts mature into osteocytes.
B. This is a soft tissue found inside bones that is involved in the production of blood cells (red, white, and platelets in red marrow) and fat storage (in yellow marrow). It is not a type of bone cell.
C. These are large, multinucleated cells responsible for bone resorption (breaking down bone tissue). They work in balance with osteoblasts to remodel and maintain healthy bone structure.
D. Osteocytes are mature bone cells that originate from osteoblasts once they become embedded in the bone matrix. They maintain bone tissue but do not actively form new bone.