Which of the following are types of conduit used in air conditioning systems?

The types of conduit typically used in air conditioning systems include EMT (Electrical Metallic Tubing), PVC (Polyvinyl Chloride), and flexible conduit. EMT is commonly used due to its strength and durability, making it suitable for protecting electrical wires in more industrial or commercial settings. PVC is favored in applications where moisture or corrosion is a concern, as it is resistant to both water and chemical damage. Flexible conduit is valuable in installations where flexibility and adaptability are required, such as in tight spaces or when connecting moving parts.

The other options contain types of materials or conduits that are either not standard for air conditioning systems or are not the correct combinations relevant to HVAC applications.