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
Ventouse application, the prerequisite is : 
Select and explain. 
A. Full dilatation of cervix, B. Station +2, C. Premature, D. Head engaged
D: Head engaged
Answer: D: Head engaged 
Explanation: Head engaged