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
If both the ala of the sacrum are absent, Charecteristic of 
Select and explain. 
A. Naegele pelvis, B. Robert pelvis, C. Triradiate pelvis, D. Rachitic pelvis
B: Robert pelvis
Answer: B: Robert pelvis 
Explanation: A pelvis that is narrowed transversely due to the entire absence of both the alae of sacrum is charecteric of Robert's pelvis