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 the presentation which lies over the Internal 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 segment of uterus
C: Bony fixed point of reference on presenting pa
Answer: C: Bony fixed point of reference on presenting pa 
Explanation: Denominator : It is an arbitrary bony fixed point on the presenting pa which comes in relation with the various quadrants of maternal pelvis. Denominators in different presentations : Occiput in veex Mentum in chin Frontal eminence in brow Sacrum I'm breech Acromion in shoulder. Ref: Datta Obs 9e pg 70.