The suggested answer is C.
Common files on a web server that can be misconfigured and provide useful information for a hacker, such as verbose error messages, include php.ini. The php.ini file is the configuration file for PHP and controls various settings, including error reporting. If misconfigured to display verbose errors, it can reveal sensitive information such as file paths, database details, and debugging information that could be exploited by attackers. Therefore, php.ini is a critical file in this context.