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
Casein, the milk protein is 
Select and explain. 
A. Nucleoprotein, B. Chromoprotein, C. Phosphoprotein, D. Glycoprotein
C: Phosphoprotein
Answer: C: Phosphoprotein 
Explanation: Phosphoproteins: These contain phosphorus. Casein of milk and vitellin of egg yolk are examples. The phosphoric acid is esterified to the hydroxyl groups of serine and threonine residues of proteins.
Reference: Vasudevan 7th  ed, pg 43