C. Suddenly he discovered something. One of his upper front teeth was loose.
Explanation:
This is the sentence that shows that Tom is extremely resourceful. We learn that Tom is trying to find a way in which he can get out of going to school. However, he cannot find any way to do so effectively. Nevertheless, Tom soon realizes that his tooth is loose, and he concludes that this is a good thing to use if he wants to get out of going to school. This shows his creativity and resourcefulness.
