The correct answers are B and D. IAM users are created for individuals who need to access AWS resources, and they can be used to sign in to the AWS Management Console or to make programmatic requests to AWS services. IAM users are also suitable when multi-factor authentication is required or when users need to access resources using the AWS API or CLI. IAM roles, on the other hand, are used to grant permissions to AWS resources or services, and they are often used for granting temporary access or cross-account access. Options A and C are incorrect because IAM roles can be attached to EC2 instances and used in mobile applications through AWS STS APIs. Option E is also incorrect as IAM roles can be used with identity federation to provide single sign-on capabilities.