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: Medicine
[{'content': 'B cell functions is tested by all of the following except ? \nSelect and explain. \nA. C H 50 count, B. Amount of Ig G, C. PPD testing, D. Cytokine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]