The AWS account root user has the highest level of permissions in an AWS account and can perform tasks that are not typically available to other IAM users. The correct answers are A and E. Option A, 'Changing an AWS Support plan', is a task that can only be performed by the root user as it involves modifying the service level of support for the entire AWS account. Option E, 'Closing an AWS account', is also a task that can only be performed by the root user, as it is a permanent action that deletes all resources and data associated with the account. Options B, C, and D are not restricted to the root user and can be performed by IAM users with the appropriate permissions.