Step 1: Idiom meaning
"Hit the nail on the head'' means to be exactly right about something — especially in analysis or judgment.
Step 2: Evaluate the context
The professor's analysis being "insightful'' supports the idea that he was spot-on.
Step 3: Eliminate other options
- Option A: Opposite of what idiom means.
- Option B and C: Not related to correctness or insight.
Only Option D matches the idiom's true meaning.