The purpose of a tape backup method is to protect and/or restore lost, corrupted, or deleted information, thereby preserving the data integrity and ensuring availability.
All other choices could suffer from corruption and it might not be possible to restore the data without proper backups being done.
This is a tricky question, if the information is lost, corrupted, or deleted only a good backup could be use to restore the information. Any synchronization mechanism would update the mirror copy and the data could not be recovered.
With backups there could be a large gap where your latest data may not be available. You would have to look at your Recovery Point Objective and see if this is acceptable for your company recovery objectives.
The following are incorrect answers:
Mirroring will preserve integrity and restore points in all cases of drive failure. However, if you have corrupted data on the primary set of drives you may get corrupted data on the secondary set as well.
Remote Journaling provides Continuous or periodic synchronized recording of transaction data at a remote location as a backup strategy. (http://www.businessdictionary.com/definition/remote-journaling.html) With journaling there might be a gap of time between the data updates being send in batch at regular interval. So some of the data could be lost.
Database shadowing is synonymous with Mirroring but it only applies to databases, but not to information and data as a whole.
Reference(s) used for this question: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, 2001, John Wiley & Sons, Page 68.