The correct answer is D. Reader.
The Reader role in Defender for Cloud allows users to view recommendations, alerts, a security policy, and security states, but cannot make changes. This is the least privileged role that allows User1 to export alert data from Defender for Cloud.
The other options are incorrect.
Option A: The User Access Administrator role allows users to manage user access to Defender for Cloud. It does not allow users to export alert data.
Option B: The Owner role allows users to do everything that the Reader role allows, plus they can make changes to the security policy and recommendations. This is more privileged than necessary.
Option C: The Contributor role allows users to do everything that the Reader role allows, plus they can apply recommendations and dismiss alerts. This is more privileged than necessary.