This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Anatomy
Denominator refers to 
Select and explain. 
A. Pa of presentation lying over the int os, B. Relation of different pas of fetus to one another, C. Bony fixed point of reference on presenting pa, D. Pa of fetus lying in the lower segmebt of uterus
C: Bony fixed point of reference on presenting pa
Answer: C: Bony fixed point of reference on presenting pa 
Explanation: Bony prominence on the presenting pa is the denominator