input: The following are multiple choice questions (with answers) about medical knowledge.   **Question:** A 3-month-old boy presents to his pediatrician with persistent diarrhea, oral candidiasis, and signs and symptoms suggestive of respiratory syncytial virus (RSV) pneumonia. His weight is in the 10th percentile. He is being evaluated for an immunodeficiency disease. Laboratory results for the HIV are negative by PCR. Which of the following is the most likely cause of these findings in this patient?   (A) Defective T cell function   (B) Grossly reduced levels of B cells   (C) Defective isotype switching   (D) Selective IgA deficiency
output: ['(A) Defective T cell function <> answer', 'The following are multiple choice questions (with answers) about medical knowledge. <> instruction', '(A) Defective T cell function  (B) Grossly reduced levels of B cells  (C) Defective isotype switching  (D) Selective IgA deficiency <> possible answers', '  A 3-month-old boy presents to his pediatrician with persistent diarrhea, oral candidiasis, and signs and symptoms suggestive of respiratory syncytial virus (RSV) pneumonia. His weight is in the 10th percentile. He is being evaluated for an immunodeficiency disease. Laboratory results for the HIV are negative by PCR. Which of the following is the most likely cause of these findings in this patient? <> context']