The correct option is A an ester group
Fats are made up of fatty acid and glycerol. The fatty acid chains form an ester bond with glycerol to form fats. This process is called esterification. Formation of ester group is a distinctive and characteristic feature of fats.
A short chain of amino acids is called peptide group.
Ketoses are examples of organic compounds with a ketonic group (C=O).
An alcoholic group is a class of organic compounds that contains an hydroxyl group (OH).