Answer: Option 'A' is correct.
Step-by-step explanation:
When a child breaks a bone, Osteoblasts is responsible for rebuilding new bone tissue in the fracture while it heals.
Because Osteoblasts build new bone if bones get broken somehow.
The new bone that built by Osteoblasts is known as "Osteoid", which is composed of bone collagen and other protein.
They control mineral and calcium decomposition.
Osteoblasts are found on the surface of new bone.
Hence, Option 'A' is correct.