Which three statements are true about sequences in a single instance Oracle database?

Sequences are database objects used to generate unique numeric identifiers. Here's the correct understanding of sequences in Oracle:

A: Correct. Cached sequence values that are not yet used are lost if the database instance shuts down, as the cache is held in memory.

B: Incorrect. The same sequence can be used to generate keys for more than one table. There is no such limitation.

C: Correct. If a transaction using a sequence number is rolled back, the sequence number that was used or allocated is not reused.

D: Incorrect. By their nature and configuration, sequences are designed to avoid issuing duplicate values unless explicitly designed to cycle.

E: Correct. Sequences may have gaps, which can occur due to caching, sequence increment settings, or if a transaction using a sequence number is rolled back.

F: Incorrect. A sequence can be dropped by any user with adequate privileges, not just a DBA.