This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'Von Willebrand factor is produced by \nSelect and explain. \nA. Liver, B. Platelets, C. Lungs, D. Spleen', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Von Willebrand factor is produced by platelets and endothelial cells Ref: Ganong 25th ed/page 565', 'role': 'assistant'}]