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
True about coronory sinus: 
Select and explain. 
A. Remnant of left horn of sinus venosus, B. Great, middle & small cardiac vein drain into it, C. Thebesian valve guard its opening, D. All
D: All
Answer: D: All 
Explanation: 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