clear glass and green glass. paper cups and plastic cups. iron nails and aluminum nails. sand and salt.
I gave my students this multiple choice question: A strong magnet will separate a mixture of

Only one answer is correct among these 4 choices:
- clear glass and green glass.
- paper cups and plastic cups.
- iron nails and aluminum nails.
- sand and salt.

Could you tell me which one is correct?

iron nails and aluminum nails.