a circuit a magnet a light bulb an insulator
I gave my students this multiple choice question: Marta has a radio in her room. It requires electricity in order to play. Which of the following is necessary in order for electricity to move from the source to the radio?

Only one answer is correct among these 4 choices:
- a circuit
- a magnet
- a light bulb
- an insulator

Could you tell me which one is correct?

a circuit