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: Anatomy
Among the following, the structure that passes deep to the flexor retinaculum is: 
Select and explain. 
A. Tibialis anterior, B. Tibialis posterior, C. Peroneus brevis, D. Peroneus longus
B: Tibialis posterior
Answer: B: Tibialis posterior 
Explanation: Tibialis posterior