a space heater turned on water boiling on the stove sunlight shining through the window a metal spoon warming in a pot of hot soup
I gave my students this multiple choice question: Which is an example of conduction?

Only one answer is correct among these 4 choices:
- a space heater turned on
- water boiling on the stove
- sunlight shining through the window
- a metal spoon warming in a pot of hot soup

Could you tell me which one is correct?

a metal spoon warming in a pot of hot soup