To enable the IPv6 in a unified SRST gateway to support SIP phones, what are two supported supplementary features for an IPv6 fallback scenario?

A company has an SRST gateway running an IOS XE image. The company plans to enable the IPv6 addressing companywide.

To enable the IPv6 in a unified SRST gateway to support SIP phones, what are two supported supplementary features for an IPv6 fallback scenario? (Choose two.)
A . three-way conference
B . secure SIP lines
D . 38 fax relay
E . transcoding
F . SIP trunk

Answer: A,C

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_sip_isr4000.html