The interview followed STAR format. You'll be asked an open ended question and expected to include in your answer Situation, Task, Action, Resolution or near enough so that the interviewer can take the appropriate notes. This is the standard interview format for CAT. There were three separate one hour interviews done back to back to back. Many of the questions are vague and similar or I ended up answering different questions similarly. It's ok to reuse stories for different interviewers, but don't change the story. They will compare notes afterwards and that'll make you look untrustworthy. Best way to prepare is to look up sample questions and come up with some stories. I don't think they asked me any of the sample questions I prepared for, but I had stories ready to go. The worst thing you could is not have an answer.