This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fetus Placenta & Fetal Membrane, Subject name: Gynaecology & Obstetrics
[{'content': 'Fetal sex can be detected by USG at: \nSelect and explain. \nA. 14 weeks, B. 16 weeks, C. 18 weeks, D. 20 weeks', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. is a, i.e. 14 weeksRef. William\'s 23/e, p 79"Gender can be determined by experienced observers by inspection of the external genitalia by 14 weeks".Ref Williams Obs 23/e, p 79', 'role': 'assistant'}]