Here's an easy riddle I got from a book:
The answer to this riddle has a hole in the middle,
And some have been known to fall in it.
In tennis, it's nothing, but it can be recieved,
And sometimes a person may win it.
Though it's not seen or heard it may yet be percieved,
Like princes or bees it's in clover.
The answer to this riddle has a hole in the middle,
And without it, one cannot start over.