How does Service Bus message deduplication prevent duplicate processing?

1. A By using consumer-side idempotency only
2. ✓ B By tracking message MessageId within a configurable duplication detection window and discarding duplicates (correct answer)
3. C By using exactly-once delivery protocol
4. D By requiring unique SessionIds

Shortcut: Enable duplicate detection on a queue or topic. Service Bus stores MessageIds for the detection window (up to 7 days). Duplicate sends with the same MessageId are discarded.