All electrical receptacles MUST be ___ AFF unless otherwise noted.

The correct answer is that all electrical receptacles must be 18 inches above finished floor (AFF) unless otherwise noted. This height is established to ensure that receptacles are accessible and usable in a variety of settings, including residential and commercial environments. The 18-inch height allows for easy reach while standing or sitting, accommodating both general accessibility standards and building codes.

In addition to practical accessibility, this height helps minimize the risk of accidental disconnection or damage to cords from foot traffic, as well as ensures that the receptacles are not too low to the ground where they might collect debris or water.

The other options do not align with the common standards or codes for receptacle installation heights that are generally accepted across most jurisdictions. While there are specific instances where different heights may be applied (such as in specialized environments or for certain types of installations), 18 inches remains the standard height unless specified otherwise by additional notes or requirements in the project documentation.