You have an application running on an Amazon EC2 instance, and you are using IAM roles to access AWS Service APIs securely. How can you configure your application running on that instance to retrieve the API keys for use with the AWS SDKs?

Answer options:

A.When assigning an EC2 IAM role to your instance in the console, in the “Chosen SDK” drop-down list, select the SDK that you are using, and the instance will configure the correct SDK on launch with the API keys.
B.Within your application code, make a GET request to the IAM Service API to retrieve credentials for your user.
C.When using AWS SDKs and Amazon EC2 roles, you do not have to retrieve API keys explicitly. Because the SDK handles retrieving them from the Amazon EC2 MetaData service.
D.Within your application code, configure the AWS SDK to get the API keys from environment variables. Because assigning an Amazon EC2 role stores keys in environment variables on launch.

Answer – C
IAM roles are designed so that your applications can securely make API requests from your instances without requiring you to manage the security credentials that the applications use. Instead of creating and distributing your AWS credentials, you can delegate permission to make API requests using IAM roles. 
For more information on Roles for EC2, please refer to the below link:
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/iam-roles-for-amazon-ec2.html