The correct answer is D. Connect a wrist strap to a metal frame, because this action directly prevents electrostatic discharge (ESD), which is one of the most common causes of accidental hardware damage during device disassembly. Even when a device is powered off, static electricity stored in the technician’s body can discharge into sensitive components such as RAM, CPUs, and system boards.

According to the Quentin Docter – CompTIA A+ Complete Study Guide, the most effective way to prevent ESD is to equalize electrical potential between the technician and the device. An ESD wrist strap, when connected to a grounded metal surface such as a computer chassis, safely dissipates static electricity before it can damage components.

The Travis Everett & Andrew Hutz – All-in-One Exam Guide explains that while antistatic mats and bags are useful, they are secondary controls. The wrist strap provides continuous grounding throughout the repair process, whereas mats and bags only protect components when they are placed on or inside them.

The Mike Meyers / Mark Soper Lab Manual reinforces that working on plastic surfaces does not guarantee grounding, and placing components in antistatic bags is something done after removal, not immediately after powering down.

Therefore, once the device is turned off, the next and most important step is to connect a wrist strap to a metal frame, making D the correct answer.