This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Characteristics of glycoprotein -a) Protein linked with glycosidic bondb) Core proteinc) Sugar residues are long in carbohydrate portion of glycoproteind) Participate in cell surface recognition 
Select and explain. 
A. b, B. c, C. ac, D. ad
D: ad
Answer: D: ad 
Explanation: The oligosaccharide units of a glycoprotein are covalently linked to the polypeptide by specific glycosidic bond, termed as the glycopeptide bond.
Core protein is found in proteoglycans, not in glycoproteins.
The length of the oligosaccharide chain is relatively short (2-10 sugar residues) in glycoproteins, whereas it is longer (upto 100) in proteoglycans.
Glycoproteins participate in cell surface recognition