The correct option is C Glycoproteins
Glycoproteins are the principal organic constituents of mucus in saliva. Mucins are high molecular weight glycoproteins which includes peptide core (apomucin) enriched in serine, threonine and proline residues. It also contains carbohydrate side chains that are linked O-glycosidically to threonine or serine.
So, the correct answer is - Glycoproteins.