Your company has implemented a multi-regional, highly available (HA) PostgreSQL database cluster on Google Cloud by using Cloud SQL and regional persistent disks. You need to assess the effectiveness of your disaster recovery plan and validate the system's ability to recover from a regional outage. What should you do?

A. Promote the cross-region replica and verify that the application can still access the database. B. Initiate a failover test to the HA standby instance and verify that the application can still access the database. C. Create a backup of the database and restore it to a new Cloud SQL instance in a different region to test the backup and restore process. D. Conduct a chaos engineering experiment by randomly terminating virtual machines in the primary region and observing the system's behavior.