Professional Speaker Fred Miller suggests you resist the urge to throw out to the audience questions you can't answer. Instead, let the person asking the question know you will follow up with them on that question after the presentation. This way you avoid both giving up control of your presentation and possibly getting the audience fighting over different answers to the question.
Controlling,
Tim Wilson
Professional Speech Coach
Free speaking tips at: http://speakingquicktips.blogspot.com
