The correct answer is C because creating a snapshot and then a new disk from that snapshot in the desired zone is the most straightforward and efficient method to replicate a disk across zones. This approach leverages GCP's snapshot functionality to ensure data integrity and availability.

• Option A is incorrect because gcloud does not support direct disk copying across zones.
• Option B involves unnecessary steps by first creating the disk in the original zone before moving it.
• Option D is incorrect as it moves the existing instance rather than creating a replica, which does not meet the high availability requirement.