This is one question to which you really ought to have a well thought-out answer, because it shows the interviewer you're goal oriented and you plan for the future, and this job you're applying for is a part of that plan. In your response, appeal to the needs and desires of the employer, which include commitment, stability and ambition. Employers will give you greater consideration if you can ensure them that their investment in you will be good for their business. Indicate your intention to stay with this company long-term and express your desire to excel as an administrative professional.