Which configuration command is needed to complete the configuration and solve the problem?

A user has reported that keys pressed when accessing Cisco Unity Express are not being acknowledged by the system.

This configuration is found on the voice-enabled IOS router:

dial-peer voice 6800 voip destination-pattern 5…

session protocol sipv2

session target ipv4:10.3.6.127

codec g711ulaw

no vad

Which configuration command is needed to complete the configuration and solve the problem?
A . dtmf-relay sip-notify
B . dtmf-relay rtp-nte
C . dtmf-relay cisco-rtp
D . dtmf-relay h245-signal