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
How many days after ovulation is placental circulation established : 
Select and explain. 
A. 18-21, B. 11-Sep, C. 9-Jul, D. 30-33
A: 18-21
Answer: A: 18-21 
Explanation: 18-21