Question time is the death of many a well intended presentation for mainly two reasons:
1. The presenter positions question time at the end of the presentation
2. The presenter is drawn into an argument and becomes defensive.
Here are two simple remedies.
First, allow yourself time for a strong summary and conclusion after question time. Second, when each question is asked, repeat the question in summary form so that the rest of the audience gets to hear it and you get a few extra seconds to construct a reply.