It's BE.
Why E? Oracle strongly recommends the use of locally managed tablespaces instead of dictionary managed tablespaces as of 10g. And it you do have dictionary managed tablespaces) then you should ideally covert it/them to locally managed tablespace(s) for ease of use and management.
B, E
You may try and succeed :
backup as compressed backupset device type disk database section size 100m; (not A,
not D).
If they speak about Unused block compression then :
RMAN skips reading, and backing up, any database blocks that are not currently allocated to some database object. This is regardless of whether those blocks had previously been allocated (bellow HWM). (Not C)
data file has to be locally managed. (E)
I believe that the options chosen should be B and C. Based on the following reference it is clear that blocks below the watermark are not included in the backup and that there is CPU overhead in the backup operations with compression.
https://docs.oracle.com/en/database/oracle/oracle-database/19/bradv/rman-backup-concepts.html#GUID-50F8DBCD-C285-491F-B8E7-E1B2140E1B51
As documentation says "When employing unused block compression, RMAN skips reading, and backing up, any database blocks that are not currently allocated to some database object. This is regardless of whether those blocks had previously been allocated." so you are wrong unfortunetally.
A is not correct - compression can be used WITHOUT writing to media, just in VALID command also:
backup as compressed backupset validate database;
Starting backup at 21-MAY-21
...
B is CORRECT
C is not correct - it is introduced in 10g unused block compression
D is not correct - checked in practice zillion times
E - is correct only for introduced in 10g unused block compression, anyway it is correct
... so I would go with B and E
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