You are planning on using the Amazon RDS facility for Fault tolerance for your application. How does Amazon RDS multi Availability Zone model work?

Answer options:

A.A second standby database is deployed and maintained in a different availability zone from the master using synchronous replication.
B.A second standby database is deployed and maintained in a different availability zone from the master using asynchronous replication.
C.A second standby database is deployed and maintained in a different region from the master using asynchronous replication.
D.A second standby database is deployed and maintained in a different region from the master using synchronous replication.

Answer – A
Amazon RDS Multi-AZ deployments provide enhanced availability and durability for Database (DB) Instances, making them a natural fit for production database workloads. When you provision a Multi-AZ DB Instance, Amazon RDS automatically creates a primary DB Instance and synchronously replicates the data to a standby instance in a different Availability Zone (AZ). Each AZ runs on its own physically distinct, independent infrastructure, and is engineered to be highly reliable. In case of an infrastructure failure, Amazon RDS performs an automatic failover to the standby (or to a read replica in the case of Amazon Aurora), so that you can resume database operations as soon as the failover is complete.
The below diagram from the AWS documentation shows how this is configured.
Option B is invalid because the replication is synchronous.
Option C and D are invalid because this is built around AZ and not regions.
For more information on Multi-AZ RDS, please visit the below URL:
https://aws.amazon.com/rds/details/multi-az/