Final Answer:
Cloud SQL is the database service that presents a MySQL or PostgreSQL interface to clients. This is evident from Cloud Platform's offering, where Cloud SQL supports both MySQL and PostgreSQL databases. The service is designed to provide a fully managed, highly available, and scalable database solution with compatibility for these popular relational database management systems. The correct answer is a) Cloud SQL.
Step-by-step explanation:
Cloud SQL is a fully-managed relational database service provided by Cloud Platform (GCP). It supports MySQL and PostgreSQL, offering clients the flexibility to choose between these two widely used database management systems. The subscript notation (MySQL or PostgreSQL) in the question indicates that the correct answer is a service supporting either of these options.
In contrast, Cloud Spanner, though a powerful database service from Cloud, is not associated with MySQL or PostgreSQL interfaces. Cloud Spanner is a globally distributed, horizontally scalable database that falls under the category of globally distributed, horizontally scalable databases, making it distinct from the traditional MySQL and PostgreSQL interfaces mentioned in the question.
In conclusion, the answer is a) Cloud SQL, as it aligns with the requirement of presenting a MySQL or PostgreSQL interface to clients. This choice is based on the understanding of the database services provided by Cloud Platform and their compatibility with the specified database systems.