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: Surgery
Cleft in facial region; 
Select and explain. 
A. Non fusion of ectodermal process, B. Absence or deficiency of mesodermal mass or other failure to penetrate ectodermal grooves, C. Covering of mesoderm on both sides by ectodermal process, D. Failure of endodermal structures to fuse in midline
B: Absence or deficiency of mesodermal mass or other failure to penetrate ectodermal grooves
Answer: B: Absence or deficiency of mesodermal mass or other failure to penetrate ectodermal grooves 
Explanation: None