What is the outcome?

You have successfully taken a database backup by using the command:
RMAN> BACKUP AS BACKUPSET DATABASE;
Now you execute this command:
RMAN> BACKUP INCREMENTAL LEVEL 1 DATABASE;
What is the outcome?

A.
It fails because an incremental level 1 backup always searches for an image copy as level 0 backup.

B.
It fails because an incremental level 0 backup does not exist.

C.
It takes a backup of blocks that have been formatted since the last full database backup.

D.
It takes an incremental level 0 backup of the database.

E.
It first takes an incremental level 0 backup and then an incremental level 1 backup.

Explanation:
https://docs.oracle.com/cd/B19306_01/backup.102/b14192/bkup004.htm (4.4.1.2)