Which value in the Application column indicates UDP traffic that did not match an App-ID signature?

Which value in the Application column indicates UDP traffic that did not match an App-ID signature?
A . not-applicable
B . incomplete
C . unknown-ip
D . unknown-udp

Answer: D

Explanation:

To safely enable applications you must classify all traffic, across all ports, all the time. With App-ID, the only applications that are typically classified as unknown traffic―tcp, udp or non-syn-tcp―in the ACC and the Traffic logs are commercially available applications that have not yet been added to App-ID, internal or custom applications on your network, or potential threats.

https://docs.paloaltonetworks.com/pan-os/9-0/pan-os-admin/app-id/use-application-objects-in-policy/create-a-custom-application