To regain access to the encrypted home folder of a user who has forgotten their login password after upgrading a Snow Leopard Mac to Mountain Lion, you can follow these steps: At the Login Window, enter an incorrect password three times in a row. When the "forgot your password" dialog appears, click the Arrow next to Master Password. Then, enter the master password, which will allow you to reset the user account password and regain access to the encrypted home folder.

In a default OS X Mountain Lion installation, the permission assigned to the top level of each user's home folder to make it accessible to Guest users who log in locally is "Everyone has Read only access." This means that Guest users can view the contents of the home folder, but they cannot make any changes or modifications to the files within it.

To start up an OS X Mountain Lion computer in Safe Mode, you need to hold down the Shift key during startup. This will prevent certain software and startup items from loading, allowing you to troubleshoot and fix any issues with your computer. It is a common method used to diagnose and resolve problems with the operating system.

The correct answer is to choose About This Mac from the Apple menu, and then click the text directly under OS X until the build number is revealed. This option allows the user to access the system information and find the build number of the OS X Mountain Lion.