conduction gravitation induction insulation
I gave my students this multiple choice question: A negatively charged rubber rod was brought near some small pieces of paper. The rod's charges repelled the negative charges in the pieces. Which of the following caused the repulsion of the negative charges?

Only one answer is correct among these 4 choices:
- conduction
- gravitation
- induction
- insulation

Could you tell me which one is correct?

induction