What does it mean if an object's `id` is a URN (e.g., `urn:uuid:…`) in ActivityPub context? - It's an error, IDs must be HTTP URLs [incorrect answer, selected] - It's a temporary object not meant for federation - It's universally unique but not necessarily dereferenceable via HTTP [correct answer] - It's an object that can only be accessed via a specific application Incorrect. The correct answer is: It's universally unique but not necessarily dereferenceable via HTTP. Explanation: While HTTPS URLs are common for `id`s to aid federation, URNs can provide global uniqueness without implying HTTP dereferencability. This might be used for objects not intended to be fetched directly over HTTP by any server.

Question 15 of 20: If an ActivityPub server cannot resolve an actor's ID (e.g., due to DNS failure), how should it typically handle activities from that actor? - Forward activities to a known relay - Temporarily queue activities and retry resolution later [incorrect answer, selected] - Assume the actor is valid and process activities - Reject activities or treat the actor as unknown/untrusted [correct answer] Incorrect. The correct answer is: Reject activities or treat the actor as unknown/untrusted. Explanation: If an actor's identity cannot be verified by resolving their ID (which is often their profile URL), a server may choose to reject or ignore activities from them for security and authenticity reasons.