The accurate statements about debug logs are:
Option A: System debug logs are retained for 24 hours.
Reference:
"Debug logs are retained for 24 hours. After that, they're deleted."
- Salesforce Help: View Debug Logs
Option B: Only the 20 most recent debug logs for a user are kept.
"A maximum of 20 debug logs are retained for each user. If there are already 20 logs, the oldest log is overwritten."
- Salesforce Help: Log Limits
Option C: Debug log levels are cumulative, where FINE log level includes all events logged at the DEBUG, INFO, WARN, and ERROR levels.
"Each log level includes all events with higher severities. For example, the DEBUG level includes ERROR, WARN, and INFO events."
- Salesforce Developer Guide: Trace Flags
Why Other Options Are Incorrect:
Option D: While you can set debug logs for specific users, you cannot set them directly for specific classes and triggers. Instead, you use trace flags associated with users, Apex classes, or Apex triggers.
Option E: The maximum size of a debug log is 20 MB, not 5 MB.
"When the debug log exceeds the 20 MB maximum size, Salesforce truncates the log. Truncated logs end with a message similar to '... truncated'."
- Salesforce Help: Debug Log Limits