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: Physiology
[{'content': 'In blood bilirubin is with \nSelect and explain. \nA. Protein, B. Steroid, C. Vitamin, D. Carbohydrates', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Bilirubin is bound to protein for transportation in blood.', 'role': 'assistant'}]