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
[{'content': 'Engaging diameter of well flexed head in vertex presentation is - \nSelect and explain. \nA. Suboccipito - bregmatic, B. Suboccipito - frontal, C. Occipito - frontal, D. Mento - vertical', 'role': 'user'}, {'content': "Answer: A \nExplanation: 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", 'role': 'assistant'}]