You must assign each server to at least _____ security group

A.
3

B.
2

C.
4

D.
1

Explanation:
Your AWS account automatically has a default security group per region for EC2-Classic.
When you create a VPC, we automatically create a default security group for the VPC. If you
don’t specify a different security group when you launch an instance, the instance is
automatically associated with the appropriate default security group.
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-network-security.html