This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fetal Skull and Maternal Pelvis, Subject name: Gynaecology & Obstetrics
Engaging diameter of well flexed head in vertex presentation is - 
Select and explain. 
A. Suboccipito - bregmatic, B. Suboccipito - frontal, C. Occipito - frontal, D. Mento - vertical
A: Suboccipito - bregmatic
Answer: A: Suboccipito - bregmatic 
Explanation: Ans. is 'a' i.e., Suboccipito - bregmatic DiametersMeasurement in cmAttitude of the headPresentationSuboccipito - bregmatic9[?]5 cmComplete flexionVertexSuboccipito - frontal10 cmIncomplete flexionVertexOccipito - frontal11[?]5 cmMarked deflexionVertexMento - vertical14 cmPartial extensionBrowSubmento - vertical11[?]5 cmIncomplete extensionFaceSubmento - bregmatic9[?]5 cmComplete extensionFace