Wiring methods permitted in ceiling areas used for environmental air include ______.

The correct answer encompasses all the options listed, which are all wiring methods permitted in ceiling areas used for environmental air. These areas include spaces where air is circulated for heating, cooling, or ventilating purposes.

Electrical metallic tubing (EMT) provides excellent protection for conductors and is suitable for both structural support and the containment of electrical wiring in these settings. Flexible metal conduit (FMC) is allowed in varying lengths, making it versatile in installation where movement or adjustments may be necessary. Rigid metal conduit (RMC), especially without an overall nonmetallic covering, is also permitted as it offers durability and strength, which is essential in protecting conductors in ceiling spaces.

Each of these wiring methods satisfies specific code requirements, ensuring safety and functionality in environmental airspaces. Therefore, the choice that includes all of these options is correct, as they all meet the necessary criteria for wiring in such areas.