To find out if the customer is experiencing problems with its IP-enabled PBX because of an overtaxed TDM bus, which question is the best to ask?

A.
Are you experiencing a delay in receiving a dial tone or is there no dial tone at all?

B.
Is the sound quality of your calls becoming increasingly worse?

C.
Are you unable to make long-distance calls at certain times of the day?

D.
Are you experiencing any echoing noise during calls?