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 can be diagnosed by all except \nSelect and explain. \nA. Measuring day 14 serum progesterone, B. Rise in basal body temperature in the second half of cycle, C. Study of cervical mucus, D. Endometrial histology', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Tests for ovulation: Basal body temperature, Endometrial biopsy, Fern test, and ultrasound.\nBut plasma concentration of progesterone rises only after ovulation and reaches its the peak of 15ng/ml by mid-luteal phase.', 'role': 'assistant'}]