What are all the possible security groups that RDS uses?

You need to set up a high level of security for an Amazon Relational Database Service (RDS) you have just built in order to protect the confidential information stored in it.

What are all the possible security groups that RDS uses?
A . DB security groups, VPC security groups, and EC2 security groups.
B . DB security groups only.
C . EC2 security groups only.
D . VPC security groups, and EC2 security groups.

Answer: A

Explanation:

A security group controls the access to a DB instance. It does so by allowing access to IP address ranges or Amazon EC2 instances that you specify.

Amazon RDS uses DB security groups, VPC security groups, and EC2 security groups. In simple terms, a DB security group controls access to a DB instance that is not in a VPC, a VPC security group controls access to a DB instance inside a VPC, and an Amazon EC2 security group controls access to an EC2 instance and can be used with a DB instance.

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