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: Surgery
[{'content': 'A 49-year-old man suffering from carcinoma of the prostate was x -rayed. He showed areas of sclerosis and collapse of T10 and T11 vertebrae in x-ray. The spread of this cancer to the above vertebrae was through - \nSelect and explain. \nA. Sacral canal, B. Lymphatic vessels, C. Internal vertebral plexus of veins, D. Superior rectal vein', 'role': 'user'}, {'content': "Answer: C \nExplanation: Prostatic cancer spreads to the bones through blood vessels; first into Batson's periprostatic venous plexus and then into the internal vertebral plexus of veins.\nThis metastasis is possible because of valveless communication between the periprostatic and vertebral plexus of veins.", 'role': 'assistant'}]