Answer:
An archaeologist unearths a coin bearing the inscription "57BC". How does he instantly know that it's a forgery?
What goes up and never comes down?
What is the building that you leave without ever having entered.
A town has only two barbers. One of the barbers has a nice, tidy haircut, and the other has a shaggy, messy haircut. Which barber should you go to?
What is yours but only used by others?
By Moon or by Sun, I shall be found. Yet I am undone, if there's no light around