Given below is a list of scenarios：
1） A user terminates his session abnormally.
2） The connection between the server and the client application terminates because of a network failure.
3） A schema is accidentally dropped.
4） The tablespace is accidentally dropped from the database.
5） The hard disk gets corrupted and the data files in the disk are lost.
6） The database instance abnormally shuts down because of power failure. 
Which scenarios require DBAintervention to perform recovery（）