A: None-there weren't any light bulbs in the 13th century.
I don't know... I broke the lightbulb after I threw the first one.
How many pessimists does it take to change a light bulb? None - it's probably screwed it too tight anyhow!
None. The light bulb shall never burn out. (OK. It's more cathartic than funny...)
Just two. It only requires that either the people are very small or the light bulb is very large.
Does it have to be a light bulb? I've got this neat candle holder...
