The following statement refers to 1,25-dihydroxyvitamin D3 (calcitriol):

a) When rapidity of action is required, 1,25-dihydroxyvitamin D3 (calcitriol), 0.25-1 Pg daily, is the vitamin D metabolite of choice, since it is capable of raising serum calcium within 24-48 hours

b) Calcitriol also raises serum phosphate, though this action is usually not observed early in treatment

c) Undergoes enterohepatic circulation

d) All of the above