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: Orthopaedics
[{'content': 'Fracture neck femur cause of non-union \nSelect and explain. \nA. smoking, B. Poor nutrition of the patient, C. Injury to blood supply with shearing stress, D. Old age and osteoporosis', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Estimates of wall shear stress at various locations in the circulation have been level of shear stress due to alterations in blood flow rate and vessel wall diameter.in part, in vivo responses of injured or activated endothelium to shear stress.', 'role': 'assistant'}]