How many security groups will ELB create by default?

A user has created an ELB with three instances.

How many security groups will ELB create by default?
A . 3
B . 5
C . 2
D . 1

Answer: C

Explanation:

Elastic Load Balancing provides a special Amazon EC2 source security group that the user can use to ensure that back-end EC2 instances receive traffic only from Elastic Load Balancing. This feature needs two security groups: the source security group and a security group that defines the ingress rules for the back-end instances. To ensure that traffic only flows between the load balancer and the back-end instances, the user can add or modify a rule to the back-end security group which can limit the ingress traffic. Thus, it can come only from the source security group provided by Elastic Load Balancing.