An approval step must pause the workflow until a human clicks a link, potentially days later. Which Durable Functions capability supports this?

1. A Timer trigger
2. ✓ B WaitForExternalEvent with an optional timeout (correct answer)
3. C Fan-out/fan-in
4. D Retry policy

Shortcut: The human interaction pattern uses WaitForExternalEvent. The orchestration is dehydrated while waiting and rehydrated when RaiseEventAsync delivers the event, incurring no compute cost meanwhile.