<em>Interesting question. Here are the revised sentences, complete with commas (when they are needed).</em>
<em />
<em>After I finished the Chicago Marathon, my legs were tired.</em>
<em>Muhammed Ali was the greatest athlete ever.</em>
<em>My mom told me to clean my room, wash the dishes, and take out the garbage.</em>
<em>I want to listen to my iPod in class, but my teacher won't let me.</em>
<em>If I had the chance, I would change our mascot to a gorilla.</em>
<em>No, I don't want to go to Taco Bell for lunch.</em>
<em>The fireworks were fun to watch.</em>
<em>Marcus Brutus, who was tricked by Cassius, was the last conspirator to stab Caesar.</em>
<em>Antony, thinking the conspirators would kill him, fled after he saw Caesar's dead body.</em>
Answer:
Food heavily affects peoples ability to focus and learn. If our school food is improved, it can help raise our grades.
The lions symbolize<span> Santiago's lost youth as well as his pride (a group of </span>lions<span> is called a "pride"). ... Now that Santiago is no longer young, and has lost his friends, family, and strength, he sees the </span>lions<span> only in his dreams.</span>