This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Gynaecology & Obstetrics
[{'content': 'Which of the following is true regarding RU 486? \nSelect and explain. \nA. Prevents feilization, B. Has affinity for estrogen receptors, C. Single dose of 10mg prevents pregnancy in 90% cases, D. Causes delayed menstruation', 'role': 'user'}, {'content': "Answer: D \nExplanation: RU 486 (mifepristone) does not prevent feilization. It has affinity for progesterone receptors. It blocks the action of progesterone on the endometrium. It prevents implantation by causing sloughing and shedding of decidua. Single dose of 10mg prevents pregnancy in 99.1% cases. Ref: Shaw's Textbook of Gynaecology, 18th edition, p237", 'role': 'assistant'}]