-there will be time at the end of the presentation to answer your questions-so please feel free to ask me anything then.
-Don't hesitate to interrupt if you have a question.
-Please feel free to interrupt me at any time.
-Please stop me if you have any questions.
-If you need clarification on any point, you're welcome to ask questions at any time.
-Can I come back to that point later?
-I will be coming to that point in a minute.
-That's a tricky question.
-We will go into details later. But just to give you an idea of...
-I am afraid there's no easy answer to that one...
-Yes, that's a very good point.
-Perhaps we could leave that point until the questions at the end of the presentation
-I think I said that I would answer questions at the end of the presentation---perhaps you wouldn't mind waiting until then.
-I think we have time for just one more question