Three:
One to write the light bulb removal program,
one to write the light bulb insertion program, and
one to act as a light bulb administrator to make sure nobody else tries to change the light bulb at the same time.
or
If Trump gets Alzheimers his IQ will go up.
or
Only one. But he'll leave a big puddle of spit on the floor underneath him.
or
T (tea)
or
It ran out of juice!
or
The man says: "You go up there and tell him off. Go on, I'll hold your monkey for you."
or