What should you do if asked a question you aren’t prepared to answer?

answer honestly that you don’t have an answer for that
pause to gather your thoughts, then answer as best you can
avoid answering by diverting attention to something else
ask the interviewer why the question is being asked

When the interviewer asks you a question that you are not prepared to answer you should
pause to gather your thoughts, then answer as best you can

Take 2 - 3 seconds to pause to collect your thoughts. Don't take too long. It is best to say things that you are sure of and that are meaningful instead of blurting out nonsense.