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
Female sexual cycle can be best assessed by: 
Select and explain. 
A. Cytology of endometrium, B. Fern test, C. Spinnbarkeit phenomenon, D. Sex steroid profile
D: Sex steroid profile
Answer: D: Sex steroid profile 
Explanation: None