Correct Answer: DWhen dealing with exceptions in a logging strategy, it is important to log meaningful messages at the appropriate level. The 'Error' level is designed for capturing issues that must be addressed and indicate a problem that needs resolution, such as an unknown System Exception in this case. This level helps in identifying and troubleshooting problems in the process. The 'Fatal' level is reserved for severe errors that cause the application to terminate, 'Info' for general informational messages, and 'Trace' for fine-grained informational events. Therefore, 'Error' is the most suitable level for logging an unknown System Exception.