Like everyone else I also spent quite a time in preparing for the interview but the officer didn't ask any questions other than name, dob, place of birth, when did you last arrive to US and the yes/no questions. He didn't ask for any documents. Though it was scheduled for 1 hr for me, 1 hr for my wife and 1 hr for my son, it was only for 15 minutes for all 3 of us together. He told me he isn't seeing any issues in approving my case and can approve on the very same day though my status still says "Interview is scheduled". I am from WA and my interview happened at Seattle. Hope this helps.