Teacher: Johnny, give me a sentence beginning with "I".
Johnny: I is...
Teacher: No, no! Always say "I am".
Johnny: Okay. I am the ninth letter of the alphabet.
The teacher sends Johnny (yes, the very same Johnny from the above joke...he`s a bit of a keener) to the map to find North America. He finds it.
Teacher: Very good. Now, class, who discovered North America?
Class: Johnny!!!