How can a user be configured as a sudoer?

The correct method to configure a user as a sudoer involves using the visudo command to make any necessary changes to the /etc/sudoers file safely. While the provided choice suggests adding a line for a specific user group, which can work in certain contexts, it's important to clarify that the most sound practice is to directly add user configurations through visudo to avoid syntax errors that could lock out sudo capabilities.

When using visudo, you can add a specific user configuration such as "user ALL=(ALL) ALL" for granting all permissions to the user named "user". Using visudo also ensures that the text editor used to modify the file performs a syntax check before saving, which helps prevent misconfigurations. On the other hand, the option that specifies "%user" refers to a user group, which isn't applicable to individual users unless that's the intended context.

Editing /etc/sudoers directly without using visudo could lead to severe problems if any syntax errors are made, as it would impact system-level permissions. Thus, while the option might seem correct, the safest and recommended way is to use visudo, drawing attention to the distinction of ensuring code quality and avoiding errors in the configuration file.