Mixed Conditionals: I didn't study for today's test. I don't know how to answer it now.
If I had studied for today's test, I would know how to answer it now.
2nd or 3rd Conditional: I learnt how to drive last month. I got my drivers license today.
3rd Conditional - If I hadn't learnt how to drive, I wouldn't have got my drivers license.
2nd or 3rd Conditional: I am really tired right now. I can't pay attention to class.
2nd Conditional - If I wasn't/weren't tired, I could pay attention to class.