Which action should a SysOps Administrator take to accomplish this?
Add each existing account to the central organization using AWS IAM.
Create a new organization in each account and join them to the central organization.
Log in to each existing account and add them to the central organization.
Send each existing account an invitation from the central organization.
Explanations:
AWS IAM is for managing access to AWS resources and cannot be used to link accounts to an organization.
Creating a new organization in each account would not join them to the central organization. It would create a separate organization.
Logging into each account manually does not automate or streamline the process of linking to the central organization.
Sending an invitation from the central organization is the correct method to invite and link existing accounts to the central organization in AWS.