Why is an electromagnet the best kind of magnet to use for these tasks?
1) An electromagnet can pick up more kinds of metal than other types of magnets.
2) An electromagnet is the only kind of magnet large enough to lift blocks of scrap metal.
3) An electromagnet has a permanent and stable magnetic field that other magnets do not have.
4) An electromagnet can be turned on when lifting metal objects and turned off to drop them, unlike other magnets.
