The interviewer would like to know if the topics that interest you the most are a match with the pieces they will ask you to write. Be sure to respond in a way that compliments the hiring company's area of focus. For instance, if they are a sports publication, you would want to refrain from saying that you only like writing on topics related to politics. Be truthful and also tie your answer in with the work that you will be doing in this position.
"I was thrilled to see your job posting for a sports writer because I live and breathe sports. I have played many sports competitively and write a sports blog in my spare time. If I could write about anything, I would choose to focus on stories of athletes who have overcome incredible obstacles, to reach their goals."
"I like to write pieces related to history, government, and our country's political past. These topics resonate with the majority of people, including your readership, which I understand to be professionals, aged 38+. It's important to me that my pieces educate and teach while helping people to understand the social and economic issues that are most pressing today."