Each of us has some preferences. While someone loves webdesign, someone else is into designing clothes, or buildings. Some guys may love to be involved in product management, having a role of a designers while taking care of the entire project in its complexity.
However, you should forget on your own interests for a while, and think about the interests of an employer. You should say that you like to design the things they typically design in their company.
Needless to say, you have to do your homework to find the right answer. Spend some time on their website, check their portfolio, find out what kind of designs they are into, and stick to that in your interview answer. Job description will also help.
Bearing all of that, it is still tiring and dreadful to work on projects you aren’t into. I would therefor never suggest you applying for a job you do not like (based on the job description), regardless of the salary offer.
I really like webdesign, especially designing sites for mobile devices. I would love to specialize on this field, that is mobile responsive design. That is also the reason why I decided to apply for the job in your company, as I see you’re into the field.
I love creative design, and I really enjoyed browsing your portfolio. I saw a lot of creativeness in each piece of work, in each campaign you run.