This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thorax, Subject name: Anatomy
[{'content': 'Left horn of sinus venosus forms: \nSelect and explain. \nA. Coronary sinus, B. Smooth part of right atrium, C. Superior vena cava, D. Inferior vena cava', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. A Coronary sinusRef: Netter's Atlas of Human Embryology: 2012 ed. pg. 96Heart tube embryonic derivativesembryonic structureGives rise to* Proximal 1/3rd of bulbus cordisPrimitive trabeculated left ventricle* Middle 1/3rd of bulbus cordisRight and left ventricular outflow tract* Distal 1/3rd of bulbus cordis (truncus arteriosus)Ascending aorta and pulmonary trunk* Left horn of sinus venosusCoronary sinus* Right horn of sinus venosusSmooth part of right atrium* Right common cardinal nerve and right anterior cardinal nerveSVC (superior vena cava)", 'role': 'assistant'}]