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: Pathology
[{'content': 'A 28 year old female teacher is found to have a prolonged bleeding time and normal platelet count. She had a bleeding of "easy bleeding" with frequent bleeding of the gums, epistaxis, cutaneous bleeding and menorrhagia, further testing revealed a deficiency of Von willebrand factor. Which of the following thrombogenic processes involving platelets is most directly impaired? \nSelect and explain. \nA. Adhesion, B. Aggregation, C. Formation of fibrinogen bridges, D. Conformational change with activation of phospholipid surface', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Disruption of the endothelium exposes subendothelial Von willebrand factor (VWF) and collagen, which promotes platelet adherence and activation.\nDeficiency of Von willebrand factor (VWF) causes\n\n\n↓\xa0Platelet adhesion (↑ BT)\n\n\n↓ Intrinsic pathway activity (↑ aPTT)', 'role': 'assistant'}]