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': 'Endothelial cells synthesize: \nSelect and explain. \nA. Fibrinogen, B. Von Willebrands Factor, C. Factor-X, D. Factor-XII', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Von Willebrands Factor', 'role': 'assistant'}]