Chondroitin sulfate C, a component of cartilage, is a polymer that is joined together via β-1,4'-glycosidic linkages; it is composed of alternating D-glucuronic acid and N-acetyl-D-galactosamine subunits, with sulfate group attached to the carbon 6 in D-galactosamine. Draw the repeating units of chondroitin sulfate C.