A user has created a VPC with CIDR 20.0.0.0/16. The user has created one subnet with CIDR
20.0.0.0/16 in this VPC. The user is trying to create another subnet with the same VPC for CIDR
20.0.0.1/24. What will happen in this scenario?

A.
The VPC will modify the first subnet CIDR automatically to allow the second subnet IP range

B.
The second subnet will be created

C.
It will throw a CIDR overlaps error

D.
It is not possible to create a subnet with the same CIDR as VPC

Explanation:
A Virtual Private Cloud (VPC) is a virtual network dedicated to the user’s AWS account. A user
can create a subnet with VPC and launch instances inside that subnet. The user can create a
subnet with the same size of VPC. However, he cannot create any other subnet since the CIDR
of the second subnet will conflict with the first subnet.
http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Subnets.html