This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diagnosis of Pregnancy, Subject name: Gynaecology & Obstetrics
[{'content': 'Which of these embryonic structures is the earliest seen USG indicator of pregnancy : \nSelect and explain. \nA. Fetal pole, B. Fetal hea activity, C. Gestation sac, D. Fetal skeleton', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Gestational sac cardiac activity Trans vaginal scan (TVS) 4+ weeks 5+ weeks Trans abdominal scan (TAS) 5 + weeks 6 + weeks', 'role': 'assistant'}]