How should they further reduce latency for all database interactions with the least amount of effort?

For this question refer to the HipLocal case study.

HipLocal wants to reduce the latency of their services for users in global locations. They have created read replicas of their database in locations where their users reside and configured their service to read traffic using those replicas.

How should they further reduce latency for all database interactions with the least amount of effort?
A . Migrate the database to Bigtable and use it to serve all global user traffic.
B . Migrate the database to Cloud Spanner and use it to serve all global user traffic.
C . Migrate the database to Firestore in Datastore mode and use it to serve all global user traffic.
D . Migrate the services to Google Kubernetes Engine and use a load balancer service to better scale the application.

Answer: D