B is correct because Cloud Spanner is a globally distributed relational database that ensures strong consistency and high availability. It scales horizontally across regions while maintaining transactional consistency, ideal for global user bases seeking performance without added complexity. A is incorrect as Bigtable, while scalable for key-value storage, lacks Cloud Spanner's transactional consistency and global availability. C is incorrect because BigQuery with Redis is tailored for analytics, not real-time transactions. D is incorrect since Cloud SQL, despite offering cross-region replication, doesn't match Cloud Spanner's performance and consistency guarantees. Links: Cloud Spanner, Cloud SQL, BigQuery, Bigtable