John works as a CCNA Voice Associate; he is working in a company that is facing the problems of Jitter, delay, and packet loss in its VoIP network. John wants to fix all these issues, but he is unable to find the main cause of these problems. Which of the following is the most likely reason for these issues?

A.
Voice VLAN is not configured.

B.
There is lack of bandwidth.

C.
The company and the service provider are located far from each other.

D.
An audio codec is wrongly configured.