Correct Answer: B
Option A is incorrect. Key material destruction built-in delay is 24-hours and 12-hour.
Option B is correct. Key material destruction built-in delay is 24-hours.
Option C is incorrect. Ability to create external keys with EKM does not help prevent accidental deletion, but helps generate external keys using supported external key managers.
Option D is incorrect. Ability of at-will key rotation, does not help prevent accidental deletion, but allows customers to set rotation schedules to automatically generate new keys at certain fixed time intervals.
https://cloud.google.com/security-key-management#section-9