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: Orthopaedics
Prolapsed intervertebral Disc (PID) is most common at - 
Select and explain. 
A. C10C11, B. C2,C3, C. L2L4, D. L5S1
D: L5S1
Answer: D: L5S1 
Explanation: L5 - SI disc space is the most commonly involved space in disc prolapse.

"Lumbar intervertebral disc herniation is most common at L5 - SI and slightly less common at L4 - L5, and rare at L3 - L4 or above".
"The disc at L5 - Si is most commonly involved, followed in order by L4 - L5 and L3 - L4". — Pocket book of orthopaedics