a piece of wood burning a copper roof changing color rust forming on an iron fence a sheet of paper shredding
I gave my students this multiple choice question: Which is a physical change?

Only one answer is correct among these 4 choices:
- a piece of wood burning
- a copper roof changing color
- rust forming on an iron fence
- a sheet of paper shredding

Could you tell me which one is correct?

a sheet of paper shredding