You are building a mobile application that will store hierarchical data structures in a database. The application will enable users working offline to sync changes when they are back online. A backend service will enrich the data in the database using a service account. The application is expected to be very popular and needs to scale seamlessly and securely. Which database and IAM role should you use?

A. Use Cloud SQL, and assign the roles/cloudsql.editor role to the service account. B. Use Bigtable, and assign the roles/bigtable.viewer role to the service account. C. Use Firestore in Native mode and assign the roles/datastore.user role to the service account. D. Use Firestore in Datastore mode and assign the roles/datastore.viewer role to the service account.