I wonder which expression can be used in my following example?
Our teacher was a really smart person. At the second session, he know everyone's name ................
off the top of his head from the knowledge you have in your memory:
- What's the capital of Mauritania?---I don't know off the top of my head, but I could go and look it up.
If you know something such as a poem by heart, you have learned it so well that you can remember it without having to read it.
- Mack knew this passage by heart.