It's not stupid, it's more likely that you can't use your brain. In fact, human potential is infinite. You always say that you can't work out the last two questions. The big reason is that you already know that they are the last two questions, so you think they are difficult psychologically. So there was the negative idea of "I can't do it anyway". It doesn't really matter. Usually do more questions and spend more time thinking about the difficult ones. Relax your mind.