Answer: Cloud Spanner

**Correct Answer: B (Cloud Spanner)** - **A (Firestore)** is incorrect because it is a NoSQL document database, not optimized for relational data, lacking the relational querying and transactional consistency needed. - **B (Cloud Spanner)** is correct as it offers a globally distributed relational database service with automatic scaling, strong consistency, and global availability, ideal for applications with growing user bases. - **C (Bigtable)** is incorrect due to its NoSQL wide-column design, which, while scalable and high-throughput, does not support relational data modeling as effectively. - **D (Cloud SQL)** is incorrect because, despite being a reliable and scalable relational database, it requires manual configuration changes and lacks the global scalability and distributed architecture of Cloud Spanner. For more information, visit: - [Cloud Spanner](https://cloud.google.com/spanner) - [Cloud SQL](https://cloud.google.com/sql) - [Firestore](https://cloud.google.com/firestore) - [Bigtable](https://cloud.google.com/bigtable)

Author: LeetQuiz Editorial Team