Which design decouples an event producer from a variable number of consumers with no producer change?

1. A Point-to-point HTTP calls
2. ✓ B Publishing to a topic and letting each consumer create its own subscription with filters (correct answer)
3. C A shared database table
4. D Direct queue writes

Shortcut: Topic-based publish/subscribe means adding a consumer is purely a subscription operation. The publisher has no knowledge of, and needs no change for, the consumer set.