Which metric Should you use?

You are developing an Azure-hosted application that processes request messages for multiple office locations.
You create an Azure Service Bus topic named Requests. The topic has a maximum size of 5 gigabytes (GB)
and a default message time to live (TTL) of 5 minutes. You also create subscriptions named PriorityRequest
and StandardRequest and include appropriate logic to route the messages.
Users report that the application has not processed messages from PriorityRequest in several days.
You need to retrieve the number of messages in the PriorityRequest subscription.
Which metric Should you use?

A.
Subscription Length

B.
Subscription Incoming Requests

C.
Topic Incoming Messages

D.
Topic Size