Before answering, consider what you want the interviewers to know about you. Understand that whatever you are reading will be interpreted as a reflection of your interests and your reading level. Offering something at a collegiate reading level or higher will serve you better in answering this question than a young adult or MG sci-fi/fantasy or romance novel. Although there is nothing wrong with enjoying that kind of entertainment, it may not serve you well for this academic interview. Show them that you feed your mind regularly. What you offer doesn't necessarily need to be a book. It could be a paper, a study, someone else's thesis, anything.
You could score extra points by advertising you read multiple books simultaneously with ease. If you are not currently reading anything because you're devoting your attention to other priorities, share something you've recently read that impacted you. The University of Colorado states on their website that they value those who are "critical thinkers and lifelong learners." Consider this when formulating your answer.
