Read the excerpt from "Mother Tongue." And here you would be presented with a list of four possible pairs, one of which showed the same kind of relationship: red is to stoplight, bus is to arrival, chills is to fever, yawn is to boring. Well, I could never think that way. I knew what the tests were asking, but I could not block out of my mind the images already created by the first pair, "sunset is to nightfall"—and I would see a burst of colors against a darkening sky, the moon rising, the lowering of a curtain of stars. How does Tan build a central idea of her story in the excerpt?