AWS Certified Solutions Architect Associate Test 10

If you're using EC2-Classic, you must use security groups created specifically for EC2-Classic.
When you launch an instance in EC2-Classic, you must specify a security group in the same region asthe instance. You can't specify a security group that you created for a VPC when you launch aninstance in EC2-Classic.
Reference:
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-network-security.html#ec2-classicsecurity-groups