What is a placement group?

What is a placement group?

A.
A collection of Auto Scaling groups in the same Region

B.
Feature that enables EC2 instances to interact with each other via nigh bandwidth, low latency connections

C.
A collection of Elastic Load Balancers in the same Region or Availability Zone

D.
A collection of authorized Cloud Front edge locations for a distribution

Explanation:
http://aws.amazon.com/ec2/faqs/