What is a 'Soft Delete' and why is it used?

1. A A low-level system process that temporarily purges a record from the localized node cache while maintaining a permanent copy on the physical disk.
2. B An optimization strategy that removes the raw data from a row but preserves the primary key index so that the ID can be safely reused for future inserts.
3. C The pattern of marking a row with a boolean flag (e.g., `is_deleted=true`) to hide it from the application while physically preserving the record for auditing.
4. D A destructive storage operation that immediately zeroes out the targeted block on the disk to ensure that sensitive information cannot be recovered.