A Group of Amazon EC2 Instances Have Been Configured as a High

A group of Amazon EC2 instances have been configured as a high performance computing (HPC) cluster. The instances are running in a placement group, and are able to communicate with each other at network speeds of up to 20 Gbps. The cluster needs to communicate with a control EC2 instance outside of the placement group. The control instance has the same instance type and AMI as the other instances, and is configured with a public IP address. How can the Solutions Architect improve the network speeds between the control instance and the instances in the placement group?

A) Terminate the control instance and relaunch it in the placement group.
B) Ensure that the instances are communicating using the private IP addresses.
C) Ensure that the control instance is using an Elastic Network Adapter.
D) Move the control instance inside the placement group.