Which configuration fixes this problem?

After configuring a Cisco CallManager Express with Cisco Unity Express, inbound calls from the PSTN SIP trunk receive a ring tone for 20 seconds and then a busy signal instead of voicemail.

Which configuration fixes this problem?
A . Router(config)# voice service voip
Router(conf-voi-serv)#allow-connections h323 to h323
B . Router(config)#dial-peer voice 2 voip
Router(config-dial-peer)#no vad
C . Router(config)# voice service voip
Router(conf-voi-serv)#allow-connections voice-mail mod
D . Router(config)# voice service voip
Router(conf-voi-serv)#no supplementary-service sip moved-temporarily

Answer: D

Explanation:

Reference: https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cusrst/admin/sccp_sip_srst/configuration/guide/SCCP_and_SIP_SRST_Admin_Guide/srst_call_handling.html