How to politely decline an interview for a PhD program? I've applied to three US universities (A, B, C) for PhD programs. Universities A and B offered me interviews on two separate weekends, which I accepted. I then made travel arrangements with Universities A and B for interviews.

I was then offered an interview with University C on the same date as my University A interview. I asked C for an alternate date, which happened to be the same weekend as my interview with B. I informed C of this and gave them a list of dates that I was free to interview but was told that those were the only two dates possible at University C. 

I asked A and B about changing my interview date but was told that I could not since travel arrangements had already been made (through the university/a university-sponsored travel agency).

Universities A and B are both higher on my list than University C, so I've decided to decline University C's interview.

How can I do this politely? I don't want to burn any bridges with University C.



Related question: What should be done about conflicting invitations for graduate school interviews?
They seem to have all the facts already. Just tell them that you had already made travel arrangements to visit A and B on the dates that C wanted you to come out, and that you have to regretfully decline to come to C. They're not going to be mad at you.