Final answer:
Flexible metal conduit is the preferred choice for machines that vibrate during operation, providing flexibility and protection for the electrical wiring.
Step-by-step explanation:
When it comes to conduits for machines that vibrate during operation, flexible metal conduit is often the preferred choice. This type of conduit is designed to handle the movement and vibration, providing flexibility and protection for the electrical wiring. It is commonly used in industrial settings where machines and equipment are subjected to constant vibrations.
On the other hand, rigid metal conduit may not be suitable for machines that vibrate as it is less flexible and may not withstand the movement without causing damage to the wiring inside.
It is also important to note that both PVC conduit and EMT conduit are not typically used for machines that vibrate during operation.