This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
[{'content': 'Ovulation is presumed to have occurred if progesterone level is __________ on day 21 \nSelect and explain. \nA. 0.3 ng / mL, B. 3 ng / mL, C. 30 ng / mL, D. 300ng / mL', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ovulation can be safely assumed to have occurred if progesterone level exceeds 3 ng / mL on cycle day 21.', 'role': 'assistant'}]