The interviewer wants to know that you are engaged in this industry and willing to dedicate time to grow your knowledge base. Employers expect employees to stay up-to-date on their respective field, and today's technology makes this reasonably easy! List several ways that you receive your industry knowledge and stay on top of trends.
Tell the interviewer about those daily update emails you receive from professional organizations, conferences you attend, seminars you have taken, and professional organizations you are a part of.
It's a great idea to ask the interviewer what resources they refer to for industry trends. That question can start up a great conversation, and you may learn a thing or two as well.