To start a computer in Safe Mode, what must you hold while booting?

To start a computer in Safe Mode, holding down the Shift key while booting is the required action. Safe Mode is a diagnostic mode designed to help isolate problems by loading only essential system files and drivers. By holding the Shift key during startup, the operating system bypasses some startup processes and runs a minimal version of the system, which can be helpful for troubleshooting issues such as persistent software problems, driver conflicts, or startup problems.

The Shift key is specifically associated with this function in macOS, making it the correct choice for booting into Safe Mode. Understanding how different keys influence the boot process is crucial for maintaining and troubleshooting Mac computers, as each key serves specific purposes such as access to recovery features or enabling certain system tasks.