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
[{'content': 'Which of the following cannot be phosphorylated using protein kinase \nSelect and explain. \nA. Aspergine, B. Threonine, C. Serine, D. Tyrosine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Protein kinase mostly add phosphoryl group to a serine, threonine or tyrosine residues.', 'role': 'assistant'}]