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
The middle cardiac vein is located in the? 
Select and explain. 
A. Anterior interventricular sulcus., B. Posterior interventricular sulcus., C. Posterior AV groove., D. Anterior AV groove.
B: Posterior interventricular sulcus.
Answer: B: Posterior interventricular sulcus. 
Explanation: The middle cardiac vein commences at the apex of the hea; ascends in the posterior longitudinal sulcus, and ends in the coronary sinus near its right extremity.