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': 'Both beta chains of haemoglobin are abnormal in \nSelect and explain. \nA. Heterozygous sickle cell trait, B. Thalassemia major, C. Homozygous sickle cell anemia, D. Megaloblastic anemia', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]