Which Tyre?

Drew and Luis were late for their English Lit final exam. Thinking quickly, they rubbed some dirt and grease on their face and hands and agreed on an excuse. By the time they got to the room, the other students had already completed their exams and left.

“We're so sorry, Professor Morris,” said Drew, “ but on the way here, we got a flat tire, and Luis and I had to change it ourselves.”

“Come back tomorrow,” said Professor Morris, smiling. “I'll let you make it up then.”

Drew and Luis were happy with the reprieve and spent the rest of the day playing outdoors.

The following morning, they arrived on time to complete the exam. The professor put the young men in separate rooms. The students found that there was only one question on the final exam. It read simply, 'Which tire?”