What to do when you don't know the answer during Q&A in a presentation

Prop: Vitamin C effervescence pills

Method: Pop the pills into your mouth and start foaming as you attempt to attempt to answer the questions.

Aftermath: Undergo a sudden revival when lesson is over and there is no way the prof/students can bug you for an answer. Then you can buy time to google it when you're at home and come up with a super intellectual answer the next time round.