1) "I've left it at home."
2) The bag check (frantically rooting through your bag, searching for your homework that you know isn't there).
3) "I've done the wrong exercise." (You just take out any bit of homework that you have done during your time in primary school.)
4) "It's my birthday."
5) "You didn't give us any homework!" (I mean, really?)
6) "I didn't understand it."  (This could all crumble with six words: “Show me where you attempted it.”)
7) "I didn't have time. Sorry. I'll do it tonight."
8) Yes, sir! Here it is. (The best option.)

Comment:

I think that the best option is the last one. Students can be better people in their lives when they learn things. Katerina Liakopoulou