Which two statements about remote survivability are true?

Which two statements about remote survivability are true? (Choose two.)

A.
SRST supports more Cisco IP Phones than Cisco Unified Communications Manager Express in SRST mode.

B.
Cisco Unified Communications Manager Express in SRST mode supports more Cisco IP Phones than SRST.

C.
MGCP fallback is required for ISDN call preservation.

D.
MGCP fallback functions with SRST.