Which of the following would BEST support a VoIP installation?

A user wants to configure their network to support VoIP. Which of the following would BEST
support a VoIP installation?

A.
QoS

B.
POTS

C.
Wake-on-LAN

D.
VPN

Explanation:
http://www.petri.co.il/voip-quality-of-service-basics.htm