194.What is an obsolete backup set?
A. A backup set that is missing one or more backup set pieces
B. A backup that has exceeded the retention criteria and is no longer needed
C. A backup set that does not include archived redo logs
D. A backup set that can not be recovered due to corruption
E. A backup set superceded by a datafile copy
Answer: B
答案解析：
An obsolete backup is, based on the currently configured retention policy, no longer needed to satisfy data recovery goals
官方参考：http://docs.oracle.com/cd/E11882_01/server.112/e10897/backrest.htm#ADMQS0956