Choice "B" is correct. The Son-Father-Grandfather concept describes this backup file system. The most recent file is called the son, the second most recent file is called the father, and the preceding file is called the grandfather. The process includes reading the previous file, recording transactions being processed, and then creating a new updated master file.
Choice "d" is incorrect. All critical application data should be backed up somehow. This concept, while good, is not specifically related to the identified procedure.
Choice "c" is incorrect. Disk only backup relates to the medium used to backup files and not to the sequence or procedure of backup steps.
Choice "a" is incorrect. There are often systems that are never scheduled to be down and they may involve some application of the Son-Father-Grandfather concept to achieve data safeguarding objectives, however, the concept underlying the procedure is not purely systems that do not shut down.