A. A notification through the Microsoft Authenticator app - This requires an active internet connection on the mobile device, which isn't available in the described scenario.
B. Email - This might not be accessible if the user can't access their email from the remote location or if email is set up to require MFA as well.
C. Security questions - While this could work, it's generally considered less secure than other MFA methods and is not recommended as a primary method.
The verification code from the Microsoft Authenticator app (option D) provides the best balance of security and usability given the constraints of working in remote locations with limited connectivity.