This advice and more can be found in Finding Your Voice:
Unless questioners use a microphone, always repeat the question so that the broader audience can hear it.
If you do not know the answer to a question, don't waffle as you try to regain ground. Admit that you do not know the answer. Suggest the person sees you after the presentation and you will take their details and if possible get back to them with an answer.
If the questioner is antagonistic, be courteous but firm. If someone is looking for a confrontation you need to nip it in the bud as quickly as possible. Don't try to justify your position; simply, and pleasantly agree to differ.
Be aware of time, as it will literally take wings, during question time. Ask the emcee to manage question time for you by identifying speakers and watching the clock.
Mrs Mary Atkins, Speaker and Author.


