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
Common cause of retained placenta : 
Select and explain. 
A. Atonic uterus, B. Constriction ring, C. Placenta accreta, D. Poor voluntary expulsive effo
A: Atonic uterus
Answer: A: Atonic uterus 
Explanation: Atonic uterus