A _____ for a VPC is a collection of subnets (typically private) that you may want to designate for your backend RDS DB Instances.

A _____ for a VPC is a collection of subnets (typically private) that you may want to designate for your backend RDS DB Instances.
A . DB Subnet Set
B . RDS Subnet Group
C . DB Subnet Group
D . DB Subnet Collection

Answer: C

Explanation:

DB Subnet Groups are a set of subnets (one per Availability Zone of a particular region) designed for your DB instances that reside in a VPC. They make easy to manage Multi-AZ deployments as well as the conversion from a Single-AZ to a Mutli-AZ one.

Reference: http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Overview.RDSVPC.html