AWS Certified Solutions Architect Associate Test 4

DB Subnet Groups are a set of subnets (one per Availability Zone of a particular region) designed foryour DB instances that reside in a VPC. They make easy to manage Multi-AZ deployments as well asthe conversion from a Single-AZ to a Mutli-AZ one.
Reference:http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Overview.RDSVPC.html