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Here are the choices
It is not acceptable to tell your audience that you are unsure of an answer and will have to research it.
It is acceptable to allow your audience to ask questions that might refute your main points.
It is always best to answer as quickly as possible. Do not appear to have to think about the question; you will look more intelligent this way.
It is perfectly acceptable and polite to omit the question and answer section from your speech entirely, and this is a good idea if you are afraid that your audience will ask questions that you cannot answer.
If you anticipate questions that may arise from your audience in advance, you can better prepare answers and possibly address them in your speech.
It is always best to answer as quickly as possible. Do not appear to have to think about the question; you will look more intelligent this way