Answer:
D. hydroxyl; carboxy
Explanation:
A fat molecule is produced by the dehydration reaction of a hydroxyl group of glycerol backbone with the carboxyl group of fatty acid. Dehydration synthesis means this reaction will produce a water molecule as byproduct.
The glycerol backbone bound to three fatty acids through an ester linkage is produced in this reaction. This compound is called triglyceride (simplest lipid) and that's why minimum 3 fatty acids molecules are necessary to make a fat molecule.
