The correct answer is A. Microsoft Entra ID Protection . Microsoft Learn explains that Microsoft Entra ID Protection detects sign-in risk and user risk and can work with Conditional Access risk policies to automatically respond when suspicious authentication activity is identified. Microsoft documents specifically state that organizations can configure sign-in risk policies and user risk policies to automate responses such as blocking access , requiring multifactor authentication , or forcing password changes when risky activity is detected. Microsoft also notes that some very high-confidence risky sign-ins are automatically blocked by built-in protections.

The other options do not match this function. Microsoft Defender for Office 365 focuses on email, collaboration, and threat protection for tools like Exchange Online and Teams, not sign-in risk blocking. Microsoft Entra Privileged Identity Management (PIM) manages privileged role activation and governance, not risky sign-in detection. Microsoft Defender for Identity detects identity-related threats in hybrid identity environments, but the Microsoft feature used to automatically block risky sign-ins is Microsoft Entra ID Protection .