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': 'Sickle cell trait patient do not have manifestations as that of Sickle cell disease, because : \nSelect and explain. \nA. 50% HbS is required for occurrence of sickling, B. HbA prevents sickling, C. 50% sickles, D. HbA prevents polymerazitation of Hbs', 'role': 'user'}, {'content': 'Answer: A \nExplanation: . 50% HbS is required for occurrence of sickling', 'role': 'assistant'}]