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
All but one are true regarding levator ani musle 
Select and explain. 
A. Levator ani muscles constitute pelvic diaphragm, B. Contraction of levator pulls rectum and vagina towards symphysis pubis, C. Insertion of the muscle is fixed, D. Internal rotation of presenting part during delivery is assisted by levator muscles
C: Insertion of the muscle is fixed
Answer: C: Insertion of the muscle is fixed 
Explanation: The origin of levator muscle is fixed because muscle arises anteriorly from bone (pubis) and is inserted into anococcygeal raphe or coccyx, both of which are moveable.