This is the index that records changes to .conf files as of Splunk 9.0. According to the Splunk documentation1, the _configtracker index tracks the changes made to the configuration files on the Splunk platform, such as the files in the etc directory. The _configtracker index can help monitor and troubleshoot the configuration changes, and identify the source and time of the changes1. The other options are not indexes that record changes to .conf files. Option B, _introspection, is an index that records the performance metrics of the Splunk platform, such as CPU, memory, disk, and network usage2. Option C, _internal, is an index that records the internal logs and events of the Splunk platform, such as splunkd, metrics, and audit logs3. Option D, _audit, is an index that records the audit events of the Splunk platform, such as user authentication, authorization, and activity4. Therefore, option A is the correct answer, and options B, C, and D are incorrect.

1: About the _configtracker index 2: About the _introspection index 3: About the _internal index 4: About the _audit index