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
Chief extensor of knee joint in hip flexion is 
Select and explain. 
A. Rectus femoris, B. Vastus medialis, C. Vastus latralis, D. Hamstrings
A: Rectus femoris
Answer: A: Rectus femoris 
Explanation: A. i.e. Rectus femoris