What Advantage Does the Activity of Osteoblasts and Osteoclasts Impart

What advantage does the activity of osteoblasts and osteoclasts impart to vertebrates, even after growth has finished?

A) As old bones are dissolved, new bones can be formed.
B) Bone growth never finishes; it continues at a slow pace throughout life.
C) The cells allow bone to get stronger as physical demands are placed on it.
D) The cells enable bone to lengthen and shorten as needed.