All of the following are macromolecules except:
a. polysaccharides.
b. proteins.
c. fatty acids.
d. ribonucleic acids.

The correct answer is c. Fatty acids

Explanation:

There are four major types of macromolecules present in nature and that are carbohydrates(polysaccharides), proteins, lipids, and nucleic acids. These macromolecules are polymers and are made up of monomer units.  

The monomeric unit of polysaccharides is mainly glucose, of protein is amino acids, of nucleic acid is nucleotides and the monomeric unit of lipid is fatty acids. Ribosomes are macromolecules because it is made up of RNA  and proteins.

So fatty acid is a monomer which joins together to form large macromolecules like lipids. Fatty acids are made up of a hydrocarbon chain which have one attached COOH group at the terminal position.

Therefore the correct answer is c. Fatty acids.