This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Lower limb 1, Subject name: Anatomy
Which of the following forms medial boundary of the marked structure 
Select and explain. 
A. Lacunar ligament, B. Inguinal ligament, C. Femoral vein, D. Pectineus muscle
A: Lacunar ligament
Answer: A: Lacunar ligament 
Explanation: Marked structure - Femoral ring Boundaries of Femoral ring Medially - Lacunar ligament Laterally - Femoral vein Anterior - Inguinal ligament Posterior - Pectineus