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: Dental
Which one of the following is found on the crown of permanent mandibular first molars but is not found on the crowns of mandibular second molars? 
Select and explain. 
A. MB cusp., B. Distobuccal groove., C. Lingual groove., D. DB cusp.
B: Distobuccal groove.
Answer: B: Distobuccal groove. 
Explanation: DB developmental groove is not found on mandibular second molars.