View From The Top, there is no standard answer for those questions. Many people here will say if you can not think of a reason why you want to work for the airline who are interviewing you then you are not suitable for the job. They may have a point, but just think about it and be honest - you might want to work for an airline because you are attracted by the fleets, the bases, the company culture, the career prospects, the status of the company, or because its a natural progression in your career.
Just remember, what ever you say it has to come from you, and if it doesn't many interviewers will spot it and pick holes in you until you collapse or the interview is terminated whichever comes first. Have you considered attending an interview prep course?