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: Anatomy
[{'content': 'True about coronory sinus: \nSelect and explain. \nA. Remnant of left horn of sinus venosus, B. Great, middle & small cardiac vein drain into it, C. Thebesian valve guard its opening, D. All', 'role': 'user'}, {'content': 'Answer: D \nExplanation: A i.e. Remnant of left horn of sinus venosus; B i.e. Great, middle & small cardiac vein drain into it; C i.e. Thebesian valve guard its opening', 'role': 'assistant'}]