Answer: Modifying the AWS Support plan

The correct answer is B, 'Changing the AWS Support plan'. This is because certain high-level account management tasks, such as updating the AWS Support plan, require root user credentials. The root user has complete access to all AWS services and resources in the account, including the ability to change the support plan. While other tasks like viewing billing information, starting and stopping EC2 instances, and opening a support case can typically be performed by IAM users with appropriate permissions, changing the support plan is a sensitive operation that requires the highest level of access, which is why it necessitates the use of the AWS account root user credentials.

Author: LeetQuiz Editorial Team