The correct answer is B. the Microsoft 365 admin center. Microsoft documents that administrators assign product licenses to users from the Microsoft 365 admin center, including on the Active users page where you can open a user account and manage Licenses and apps. Microsoft also documents license assignment workflows there for both direct assignment and group-based licensing scenarios. That makes the Microsoft 365 admin center the standard administrative portal for giving a user access to Microsoft 365 services and features.

The other options are incorrect for this task. The Microsoft Purview portal is used for compliance, governance, data protection, eDiscovery, audit, and related Purview solutions, not for assigning Microsoft 365 product licenses. The Microsoft Teams admin center is used to manage Teams settings, policies, devices, voice, and collaboration features, but it is not the central portal for assigning tenant product licenses to users.