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': 'All the following openings in the right atrium are guarded by valve except - \nSelect and explain. \nA. Superior vena cava, B. Inferior vena cava, C. Coronary sinus, D. Atrioventricular opening', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Valves on different openings to Right atrium\n-\xa0\xa0\xa0\xa0\xa0\xa0\xa0 Inferior vena cava- Rudimentary semilunar valve- Eustachian valve\n-\xa0\xa0\xa0\xa0\xa0\xa0\xa0 Coronary sinus- Incomplete semicircular valve- Thebesian valve\n-\xa0\xa0\xa0\xa0\xa0\xa0\xa0 AV opening- Tricuspid valve', 'role': 'assistant'}]