E-mail Jokes

I tend to get irritated when people forward me jokes via e-mail on a regular basis. My parents are the worst offenders. However, I find myself reading the e-mails just in case the jokes happen to be funny.

I received one from my mom today that was about to be deleted after reading the first few sentences. However, I kept going. Maybe it was my mood at the time, but I found it somewhat creative. I'll share with all of you.
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At Northern Michigan University , there were four sophomores taking chemistry and all of them had an "A" so far. These four friends were so confident that the weekend before finals, they decided to visit some friends and have a big party. They had a great time but, after all the hearty partying they slept all day Sunday and didn't make it back to College until early Monday morning.

Rather than taking the final then, they decided that after the final they would explain to their professor why they missed it. They said that they visited friends but on the way back they had a flat tire. As a result, they missed the final.

The professor agreed they could make up the final the next day.

The guys were excited and relieved. They studied that night for the exam. The Professor placed them in separate rooms and gave them a test booklet They quickly answered the first problem worth 5 points. Cool, they thought! Each one in separate rooms, thinking this was going to be easy.... then they turned the page.

On the second page was written....

For 95 points:

Which tire? _________