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': 'Indirect coombs test detect - \nSelect and explain. \nA. Antibodies attached to RBC surface, B. Antigen in serum, C. Antibodies in the serum, D. Antigen attached to RBC surface', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]