Cloud Spanner is a globally distributed, horizontally scalable, and strongly consistent relational database service offered by Google Cloud. It provides the ability to scale both storage and compute resources as needed, ensuring consistent transaction handling across multiple regions. This makes it an ideal choice for applications that require strong consistency and high scalability.
While options A (Cloud SQL), B (Cloud Storage), and C (Firestore) are also valuable Google Cloud products, they may not meet the specific requirements mentioned in the context as effectively as Cloud Spanner. Cloud SQL is a managed relational database service, but it may not provide the same level of scalability and global consistency as Cloud Spanner. Cloud Storage is a scalable object storage solution, and Firestore is a NoSQL document database, but they may not offer the same level of transaction consistency required for managing payments and online bank accounts.