Which of the following options of AWS RDS allows for AWS to failover to a secondary database in case the primary one fails?

Answer options:

A.Amazon RDS Multi-AZ deployments
B.AWS Failover
C.AWS Secondary
D.AWS Standby

Answer – A
The AWS Documentation mentions the following.
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 it 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 you can resume database operations as soon as the failover is complete. 
Options B, C and D are the distractors because there is no AWS service like failover, standby or secondary. Failover is the situation when Multi-AZ appears and Standby or Secondary represents other RDS servers appears during Multi-AZ deployments. 
For more information on AWS RDS Multi-AZ, visit the below link:
https://aws.amazon.com/rds/details/multi-az/