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: Physiology
[{'content': 'Female sexual cycle can be best assessed by: \nSelect and explain. \nA. Cytology of endometrium, B. Fern test, C. Spinnbarkeit phenomenon, D. Sex steroid profile', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]