Knowing the right answer, or when "it depends", is not the expectation. You need to get inside the mind of the interviewer and figure out what he/she thinks is the right answer is, or guess what's probably written on the answer sheet. Think: "What answer would a know-it-all 23-year-old Stanford graduate give?" That, and not necessarily the right answer, is what will get you the job offer.
This is also called "cultural fit".