What topic could you give a 20-minute presentation on without any preparation?

Only one?
1)The fashion industry and the environmental damage it causes.
2)Martial arts and self defence.
3)Bodybuilding.
4)Why we need to stop using fossil fuels and invest in nuclear fusion.
5)Why space exploration is so important.
6)How we are affected by advertising and product placement.
7)How we have been turned into upgraders.
8)Why industry always comes out on top when they clash with environmentalists.

I can add more too.