The callus that develops at the fracture site is important because it provides:

A callus is important to a healing fracture because it encloses the fracture site, creating a temporary bridge between the bones. This is important to facilitate healing and repair for the bone. It allows the bones to slowly grow back together, and it is eventually replaced with bone tissue and reabsorbed into the body over time.

idk but if i had to take an educated guess i’d say a c d