Take two metal bars (A and B) at random, and put one end of A near the two ends of B, and then near the middle of B. ..
What happens: When 1 A is near both ends of B, the two stick together. When A approaches the middle of B, the two metal bars separate. This shows that B has magnetism at both ends and no magnetism in the middle. So b is a magnet and a is iron.
When A approaches both ends of B, everyone sticks together; When A is near the middle of B, it sticks together again. This shows that A is a magnet, and B may be iron or a magnet. At this time, Party A and Party B can jump ship! If b is not stuck together near the middle of a, it means that b is iron; If they stick together, B is a magnet.
Because you already know what two metal bars are, you can know what the third one is! !
Please adopt! ! Thank you!