[Ed: This submitter put this in rot13, nobody knows why.]

Four high school boys (and girls) afflicted with spring fever
skipped morning classes. After lunch they reported to the teacher
that they had a flat tire.

Much to their relief she smiled and
said: Well, you missed a test today so take seats apart from one
another and take out a piece of paper.

Still smiling, she waited
for them to sit down. Then she said:

First Question: Which tire was flat?