Please choose the correct answer to the 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?

Answer1: sort the cans by size Answer2: put the cans in water Answer3: cool the cans to a low temperature Answer4: put the cans under an electromagnet

Answer format: answer1/answer2/answer3/answer4