As a teacher, I learned quickly that when you don’t know something, it’s best to say you don’t know, rather than trying to fake your way to an answer. Students are curious beings, well at least they should be, and they will always question the things they want to learn. If they find out that you covered the truth somehow, you lose respect, which is already hard to earn as a teacher.

You can tell them you don’t know, or you can tell them that you need to revise. At least guarantee them an answer of sorts.