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: Pathology
[{'content': 'In sickle cell anemia there is substitution of \nSelect and explain. \nA. Valine for glutamic acid at the sixth position of beta chain, B. Phenylalanine for glutamic acid, C. Tyrosine for valine at the 6th position at beta chain, D. All of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]