Osteoporosis, an age-related disease of skeletal system, may occur due to

• A

  immune disorder affecting neuromuscular junction leading to fatigue

• B

  high concentration of ${\mathrm{Ca}}^{++}$and ${\mathrm{Na}}^{+}$

• C

  decreased level of estrogen

• D

  accumulation of uric acid leading to inflammation of joints.