The correct answer is A. the SharePoint admin center . Microsoft documents that the SharePoint admin center includes Data access governance reports and site-level sharing reports that help administrators identify where content is shared externally. Microsoft also documents that every standard Microsoft Teams team is connected to a SharePoint site for file storage and collaboration. Because Teams files and many sharing scenarios for teams are backed by SharePoint sites, the SharePoint admin center is the correct place to investigate which sites are shared externally, including Teams-connected SharePoint sites .

The other options are less suitable for this requirement. The Teams admin center is primarily for Teams policy, user, device, and workload administration, but it is not the main portal Microsoft documents for identifying externally shared site content. The Microsoft 365 admin center focuses on broad tenant administration and usage reporting, and the Microsoft Defender portal is for security investigation rather than SharePoint/Teams sharing governance. For identifying externally shared SharePoint sites and Teams-connected sites, Microsoft’s documented reporting path is the SharePoint admin center .