This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Physiology
Corpus luteum stas regressing after how many days of ovulation 
Select and explain. 
A. 5 days, B. 10 days, C. 15 days, D. 20 days
B: 10 days
Answer: B: 10 days 
Explanation: A corpus luteum is a mass of cells that forms in an ovary and is responsible for the production of the hormone progesterone during early pregnancy. The role of the corpus luteum depends on whether or not feilization occurs Ref: guyton and hall textbook of medical physiology 12 edition page number:637,638,639