Read the excerpt from "Mother Tongue."

Those tests were constructed around items like fill-in-the-blank sentence completion, such as “Even though Tom was ______, Mary thought he was _____.” And the correct answer always seemed to be the most bland combinations of thoughts, for example, “Even though Tom was foolish, Mary thought he was ridiculous.” Well, according to my mother, there were very few limitations as to what Tom could have been and what Mary might have thought of him. So I never did well on tests like that.

How does Tan build a central idea of her story in the excerpt?