This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Gynaecology & Obstetrics
[{'content': 'What is a placental cotyledon: \nSelect and explain. \nA. All branches from one stem villi, B. Area supplied by one spiral aery, C. Quaer of placenta, D. Area drained by one terminal villi', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Functional unit of the placenta is called a fetal cotyledon or placentome,which is derived from a major primary stem villus. These stem villi pass down through the intervillous space to anchor onto the basal plate.About 60 stem villi persist in human placenta. Thus each cotyledon(totalling 15-29) contains 3-4 major stem villi. Reference : Dutta Textbook of Obstetrics &th edition page no 31', 'role': 'assistant'}]