How should you manage your AWS identities in the most simple manner?

You run a 2000-engineer organization. You are about to begin using AWS at a large scale for the first time. You want to integrate with your existing identity management system running on Microsoft Active Directory, because your organization is a power-user of Active Directory. How should you manage your AWS identities in the most simple manner?
A. Use a large AWS Directory Service Simple AD.
B. Use a large AWS Directory Service AD Connector.
C. Use an Sync Domain running on AWS Directory Service.
D. Use an AWS Directory Sync Domain running on AWS Lambda