How can the user configure the access for that EC2 instance?

A user has launched one EC2 instance in the US West region. The user wants to access the RDS instance launched in the US East region from that EC2 instance.

How can the user configure the access for that EC2 instance?
A . Configure the IP range of the US West region instance as the ingress security rule of RDS
B . It is not possible to access RDS of the US East region from the US West region
C . Open the security group of the US West region in the RDS security group’s ingress rule
D . Create an IAM role which has access to RDS and launch an instance in the US West region with it

Answer: A

Explanation:

The user cannot authorize an Amazon EC2 security group if it is in a different AWS Region than the RDS DB instance. The user can authorize an IP range or specify an Amazon EC2 security group in the same region that refers to an IP address in another region.

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