To make a glycerophospholipid, fatty acids are esterified at the _
a. 1,2 position of the sn-glycerol-3-phosphate
b. 2,3 position of the sn-glycerol-3-phosphate
c. 3,4 position of the sn-glycerol-3-phosphate
d. 4,5 position of the sn-glycerol-3-phosphate