What are the configurations required for phone redundancy and self-survival?

You are discussing with a customer who has four branches and 4,000 employees. Singapore has a master data center and Sidney has a backup data center. They have branches in Los Angele and Denver. They want the phone of the branch office to self-surviving locally.

What are the configurations required for phone redundancy and self-survival? (Please choose three)
A . CM in Sydney is deployed as a self-surviving core (ESS)
B . CM instance in the Los Angele, and Denver, deployed for remote self-surviving
C . CM in the Denver is deployed as active CM instance
D . CM in Los Angeles was deployed as a self-surviving core (ESS)
E . The CM instance in Singapore and Sydney is deployed for remote self-surviving
F . CM in Singapore is deployed as active CM instance

Answer: ABF