Compact bone is composed of
trabeculae
compacted collagen
osteons
calcium phosphate only

The correct answer is C. Osteons

Explanation:

Bones are solid or rigid organs that have important functions and that are part of the skeleton in the vertebrate animals. Although bones vary according to size and shape in most cases the structure of bones is the same. This structure includes the bone marrow that is in the center; the cancellous bone that is spongy and contains red bone marrow; the cortical bone or compact bone that is the hardest layer and is composed of osteons that form columns; and the periosteum or external layer that includes collagen fiber. Therefore, the compact bone is the one composed of osteons.