Prolapsed intervertebral Disc (PID) is most common at -: (A) C10C11, (B) C2,C3, (C) L2L4, (D) L5S1
Answer is D. 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