Which of the following are features of AWS ECS? (Choose 3 options)

Answer options:

A.Task Definition
B.Tasks
C.Container Registery
D.Cluster
E.Source Image Storage

Answer: A, B, D
Here is a high-level overview of ECS service.
Following are the features for AWS ECS.
Containers and Images
Task Definitions
Tasks and Scheduling
Clusters
Container Agent
For more information on ECS features, refer documentation here. 
https://docs.aws.amazon.com/AmazonECS/latest/developerguide/Welcome.html#welcome-features
Options A, B and D are part of above feature list.
Option C is not part of ECS. Amazon Elastic Container Registry (Amazon ECR) is a fully managed Docker container registry that makes it easy for developers to store, manage, and deploy Docker container images.
For more information on AWS ECR, refer documentation here. 
https://docs.aws.amazon.com/AmazonECR/latest/userguide/what-is-ecr.html
Option E is not correct. It is part of AWS ECR.