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': 'Common variable deficiency is due to - \nSelect and explain. \nA. Absent B cells, B. Reduced number of B cells, C. Defective B cell differentiation, D. All of the above', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Most patients with common variable immunodeficiency have normal or near-normal numbers of B cells\xa0in the blood and lymphoid tissues.\nThese B cells, however, are not able to differentiate into plasma cells.\nThe clinical manifestations are caused by antibody deficiency.\nThe feature common to all patients is hypogammaglobulinemia, generally affecting all the antibody\xa0classes but sometimes only IgG.', 'role': 'assistant'}]