During a routine checkup a 70 year old male is found to have Serum Alkaline Phosphatase three time the upper limit of normal. Serum Calcium, Serum Phosphorous and liver function tests are normal. The most likely diagonsis is______________?

A. Primary hyperparathyroidism
B. Paget’s disease of the bone
C. Osteomalacia
D. Metastatic bone disease