This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Abdomen and pelvis, Subject name: Anatomy
Length of anal canal 
Select and explain. 
A. 10 - 15 mm, B. 15 - 20 mm, C. 25 - 30 mm, D. 35 - 40 mm
D: 35 - 40 mm
Answer: D: 35 - 40 mm 
Explanation: The length of the anal canal is about 4 cm (range, 3-5 cm), with two thirds of this being above the pectinate line (also known as the dentate line) and one third below the pectinate line ref - BDC 6e vol2 pg413