In Apple Business Manager (ABM), the Administrator role has broad permissions, including purchasing apps and assigning devices to MDM servers. The Content Manager (option B) can manage and distribute content (e.g., apps, books) but cannot purchase apps or assign devices. The Device Enrollment Manager (option C) focuses on enrolling and assigning devices but lacks purchasing authority. The People Manager (option D) manages user accounts, not apps or devices. The Apple Business Manager User Guide outlines the Administrator's comprehensive responsibilities, making it the correct choice.