All the following openings in the right atrium are guarded by valve except -: (A) Superior vena cava, (B) Inferior vena cava, (C) Coronary sinus, (D) Atrioventricular opening
Answer is A. Valves on different openings to Right atrium
-        Inferior vena cava- Rudimentary semilunar valve- Eustachian valve
-        Coronary sinus- Incomplete semicircular valve- Thebesian valve
-        AV opening- Tricuspid valve