heat the mixture filter the mixture pour water into the mixture pull a magnet through the mixture
I gave my students this multiple choice question: A container is filled with a mixture of sand and an unknown substance. What should a student do to determine whether iron particles are in the mixture?

Only one answer is correct among these 4 choices:
- heat the mixture
- filter the mixture
- pour water into the mixture
- pull a magnet through the mixture

Could you tell me which one is correct?

pull a magnet through the mixture