In terms of bone health, why would a physician advise an older patient to do more weight-bearing ...

In terms of bone health, why would a physician advise an older patient to do more weight-bearing activity such as walking, jogging, or use of moderate weights?

a) it promotes normal bone remodeling
b) osteoblasts deposit more minerals salts and collagen fibers as a response to mechanical stress
c) being sedentary (not physically active) promotes bone loss through resorption by osteoclasts
d) bone formation in stressed bones is stimulated by the tug of muscles (when exercising)
e) all of these explain why a physician would give such advice to a patient