This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Haematology, Subject name: Pathology
[{'content': 'Hemoglobin H disease is caused by deletion of- \nSelect and explain. \nA. A single a globin gene, B. Two a globin genes, C. Three a globin genes, D. All four a globin genes', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Moderate microcytic hypochromic anemia.People with hemoglobin H disease have a variable phenotype that can range from mild symptoms to those similar to thalassemia major. Hemoglobin H disease is a type of alpha thalassemia caused by impaired production of three of the four alpha globins, coded by genes HBA1 and HBA2 Exam preparatory manual for UGs by Ramdas Nayak Paage no:273 Ref Robbins 9/e 413', 'role': 'assistant'}]