The correct answer is C. The root user is the first sign-in identity that is available when an AWS account is created. This user has full administrative access to all resources and services within the AWS account. It is a security best practice to not use the root user for everyday tasks and to create additional IAM (Identity and Access Management) users with appropriate permissions. The root user is not the only user that can be configured with MFA (Option A is incorrect), nor is it the only user that can access the AWS Management Console (Option B is incorrect). Additionally, the root user's password can be changed, which makes Option D incorrect.