John works as a Sales Engineer for KBC Inc. He has been assigned a project to install a soft phone on different computers. One of the computer systems on the LAN is experiencing problems in voice quality. Which of the following actions should John perform to resolve the problem?

A.
Add more system RAM.

B.
Upgrade the computer system.

C.
Upgrade the Network Interface Card (NIC).

D.
Upgrade the network cable to category 6 cabling.