[Reference: https://docs.splunk.com/Documentation/ITSI/4.10.2/EA/TroubleshootRE, The index that will contain useful error messages when troubleshooting ITSI issues is:, B. _internal. This is true because the _internal index contains logs and metrics generated by Splunk processes, such as splunkd and metrics.log. These logs can help you diagnose problems with your Splunk environment, including ITSI components and features., The other indexes will not contain useful error messages because:, A. _introspection. This is not true because the _introspection index contains data about Splunk resource usage, such as CPU, memory, disk space, and so on. These data can help you monitor the performance and health of your Splunk environment, but not the error messages., C. itsi_summary. This is not true because the itsi_summary index contains summarized data for your KPIs and services, such as health scores, severity levels, threshold values, and so on. These data can help you analyze the trends and anomalies of your IT services, but not the error messages., D. itsi_notable_audit. This is not true because the itsi_notable_audit index contains audit data for your notable events and episodes, such as creation time, owner, ]