Cord-and-plug connected vending machines manufactured after January 1, 2005, must include a ground-fault circuit interrupter within __________ of the attachment plug.

The correct requirement is that cord-and-plug connected vending machines manufactured after January 1, 2005, must include a ground-fault circuit interrupter (GFCI) within 12 inches of the attachment plug. This provision ensures that the vending machine is equipped with an added layer of safety against electrical shock hazards, as GFCIs are designed to protect people from the dangers of ground faults.

The proximity requirement of 12 inches is specified to ensure that the GFCI is easily accessible, allowing for prompt resetting and enhancing user safety. This location helps to minimize the potential for electrical accidents, particularly in environments where moisture is present, such as in kitchens or laundry areas where vending machines might be located.

Other distances highlighted in the options, like 6 inches, 9 inches, or 18 inches, do not meet the safety regulations set forth in the applicable electrical codes for this type of equipment. Having the GFCI too far from the outlet could hinder timely intervention in case of a ground fault, while being placed too close doesn't provide the intended benefit in terms of accessibility and usability.