Which Windows registry hive stores file extensions for applications?

The correct answer is HKEY_CLASSES_ROOT, as this particular registry hive is specifically designed to store information about file associations, including file extensions and the applications that are associated with them. When you double-click a file in Windows, the system checks the HKEY_CLASSES_ROOT to determine which program should open that file based on its extension. This hive acts as a central point to manage how the operating system associates files with specific applications, making it crucial for functionality regarding file types and their corresponding handlers.

HKEY_LOCAL_MACHINE, on the other hand, primarily contains settings that apply system-wide, such as hardware configurations and software settings. It is not specifically focused on file associations.

HKEY_CURRENT_USER stores user-specific settings and preferences, which can include application settings, but it does not directly manage file associations in the same way that HKEY_CLASSES_ROOT does.

HKEY_CURRENT_CONFIGURATION is less commonly referenced and typically pertains to current hardware profiles, not file extension associations or application configurations. Therefore, HKEY_CLASSES_ROOT is the most appropriate answer for the storage of information related to file extensions for applications.