D
Below is a question with multiple-choice answers. Choose the correct option based on your reasoning.

### 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?

### Choices:
A. sort the cans by size
B. put the cans in water
C. cool the cans to a low temperature
D. put the cans under an electromagnet

### Answer:
