Sudden pain at the anal verge after straining suggests a perianal hematoma / thrombosed external hemorrhoid. It sits below the dentate line, which has somatic sensation and is very sensitive. The lecture slide gives this innervation as the pudendal nerve. The specific pudendal branch to that area is the inferior rectal nerve, which is written on the anatomy notes and is the bank key. Both C and D are defensible. C is the more specific answer. The obturator and hypogastric (autonomic) nerves are wrong.