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 of the following is the smallest posterior tooth: 
Select and explain. 
A. Maxillary first premolar., B. Mandibular first premolar., C. Maxillary second premolar., D. Mandibular second premolar.
B: Mandibular first premolar.
Answer: B: Mandibular first premolar. 
Explanation: Mandibular first premolar is the smallest tooth with MD diameter of 7 mm and BL.