Bone mass increases in humans until about age __________ because __________ after that time.

Bone mass increases in humans until about age
  __________ because __________ after that time.
  a. 18; osteoclast activity commences
  b. 13; osteoblast activity slows
  c. 24; osteoblast activity slows
  d. 24; osteocytes no longer function
  e. 18; osteocytes are no longer formed

Question 2

PTH (parathyroid hormone) does all of the following
  EXCEPT
  a. stimulates calcium release from bones.
  b. suppresses calcium reabsorption by the kidneys.
  c. enhances osteoclast action.
  d. activates vitamin D in the gut.
  e. indirectly stimulates calcium absorption by the
  gut.