Slack requires an application using HTTP Events API delivery to acknowledge an event request with an HTTP `2xx` response within three seconds. If Slack does not receive a successful acknowledgment in that period, the delivery attempt is treated as unsuccessful and Slack may retry the event. Slack recommends responding with `HTTP 200 OK` as rapidly as possible and separating event ingestion from potentially slow business processing. A robust production architecture typically acknowledges the request immediately, places the event on a queue, and performs downstream processing asynchronously. This prevents expensive API calls, database operations, or external-service dependencies from delaying acknowledgment and producing duplicate deliveries. Returning Block Kit content is unnecessary for acknowledgment, while user logout and scope requests are unrelated. Therefore, A is correct and represents an important Slack scalability and reliability pattern.