For a mission-critical, stateful application in your organization that demands strict consistency and high availability across multiple zones within a region, which Google Cloud service is best suited for the database layer?

*Explanation: The correct option is Cloud Spanner with a multi-zone configuration. Cloud Spanner is designed to offer strong consistency and high availability, making it ideal for mission-critical applications that require these features. Its multi-zone configuration ensures that the application remains highly available even in the event of a zone failure, as it automatically manages replicas across multiple zones. This capability is crucial for maintaining application performance and data integrity. In contrast, the other options like Cloud Bigtable, Cloud SQL, Cloud Datastore, and Persistent Disks, while useful in their own right, either do not provide the required level of strong consistency across multiple zones or are not optimized for high availability in the context of a stateful application.*