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: Unknown
Establishment of fetoplacental circulation seen at 
Select and explain. 
A. 11 to 13 days, B. 20 to 22 days, C. 7 days, D. 25 to 26 days
B: 20 to 22 days
Answer: B: 20 to 22 days 
Explanation: Ref. DC Dutta's Textbook of Obstetrics. Pg 36
 
Implantation of 12-16 cell stage occurs in the endometrium on the anterior and posterior wall of the body near the fundus on the 6th day following fertilization.

Then the deeper penetration of the human blastocyst is called interstitial implantation, which happens by approx. 13th day after fertilization
The fetal circulation is established by 21st days after fertilization