A metal rod $PQ$ is placed on two horizontal metal wires connected to a battery. The rod is positioned between the poles of a magnet. When the switch is closed, the rod moves to the right. What could be altered so that the rod moves to the left?
- AOpen the switch.
- BReverse the battery terminals and exchange the poles of the magnet.
- CReverse the battery terminals but without exchanging the poles of the magnet.
- DTurn the metal rod around ($P$ and $Q$ exchanged).