Shake the mixture, and the iron filings will rise to the surface. Add water to the mixture, and the sand will dissolve in the water. Put the mixture through a sieve, and the sand will remain in the sieve. Pass a magnet over the mixture, and the magnet will attract the iron fillings.
I gave my students this multiple choice question: Katie has a mixture of iron filings and sand. She wants to separate them. How can she do this?

Only one answer is correct among these 4 choices:
- Shake the mixture, and the iron filings will rise to the surface.
- Add water to the mixture, and the sand will dissolve in the water.
- Put the mixture through a sieve, and the sand will remain in the sieve.
- Pass a magnet over the mixture, and the magnet will attract the iron fillings.

Could you tell me which one is correct?

Pass a magnet over the mixture, and the magnet will attract the iron fillings.