sort the cans by size put the cans in water cool the cans to a low temperature put the cans under an electromagnet
I gave my students this multiple choice question: Steel cans are separated from aluminum cans in a recycling center. Which of the following is the best way the recycling center can separate the steel cans from the aluminum cans?

Only one answer is correct among these 4 choices:
- sort the cans by size
- put the cans in water
- cool the cans to a low temperature
- put the cans under an electromagnet

Could you tell me which one is correct?

put the cans under an electromagnet