Why is a transactional.id required for transactional producers, and what can happen if a transaction is not properly aborted on error?

• A. transactional.id identifies a transaction across producer restarts; failing to abort can leave an open transaction or duplicates; you must call abortTransaction on failure to cleanly rollback.
• B. transactional.id identifies a topic.
• C. transactional.id identifies a consumer group.
• D. transactional.id is optional and has no effect.

Answer: (A)