Which Statement about migration to Cisco Unified Communications is true?

A.
If something unexpected occurs, the phased migration provides a back-out plan that allows you to revert, with minimal effort, to the previous system, which is essentially still intact.

B.
A phased migration is best suited for single- site deployments, whereas a parallel cutover is better for multisite deployments.

C.
A phased migration allows you to revert, with minimal effort, to the previous system.

D.
A phased migration purchases individual components of the system as and when they are needed.