This is something that might be very difficult to answer. Whatever you choose to talk about, important to remember is to say what the outcome was and state what you learned from this experience. Don't say that you were fired!
Multitasking is a necessary part of an administration job, so say that you enjoy multitasking and the challenge of ensuring that multiple functions and jobs are completed accurately and on time is part of what motivates you in your work.
Meeting people and speaking to customers is often a vital part of being an administrator. Say that you enjoy talking to people and that interaction with other people is often what makes the work most interesting.
This is similar to "what can you bring to this organisation?"
Answer that by staying organised and keeping a strict diary you find that stress does not become a real issue. As soon as you identify a possible delay due to high work volumes you raise this with your manager to see if the work can either be reallocated or given priority.
Ideally, you will be able to touch type well, so say yes to this. Shorthand is a dying art and fewer people are learning how to do this well. If you have the opportunity to learn it, then do so, because some managers like their administrators to be able to take down shorthand.
Say that you deal with authority as you deal with customers - with integrity, professionalism and politeness.
This could be through study, training or experience. It all depends on the type of person you are and the type of skills you have.
Translates to: Is this what I want to be doing? You don't want to accept a job where you don't really know the sort of things you'll be doing, especially if you find that your daily tasks are too easy.