When your girlfriend asks you "do you think I'm stupid", it's a delicate question that needs to be answered in a way that doesn't hurt her and makes her feel understood and respected. Here are some suggestions to help you answer this question while maintaining a professional and high-quality tone and style. 
1.Avoid answering this question directlyFirst, try to avoid answering this question directly. Because whatever your answer is, it might make your girlfriend feel uncomfortable. If you answer "no", she may worry that you are just comforting her;If you answer "yes," she may feel hurt and frustrated. Therefore, the best way to do this is to adopt a tactful way of answering. 2.Praise her wisdom before answering a question, praise her for her wisdom and talent. For example, you could say, "You know what, I've always admired your ingenuity and keen insight. You are always able to see through the essence of the problem and give me a lot of valuable advice. Such an answer will not only make your girlfriend feel appreciated and respected, but also pave the way for the rest of the answer. 
3.Guide her to focus on her strengthsNext, you can guide your girlfriend to focus on her strengths instead of focusing too much on her weaknesses. For example, you can say, "Everyone has their own strengths and weaknesses, but that doesn't stop us from being good people." You have many virtues such as being diligent, attentive, caring, and so on. These advantages make you even better and more attractive. Such an answer can make your girlfriend feel understood and supported, and it can also make her more confident and determined. 
4.Encourage her to keep tryFinally, you can encourage your girlfriend to keep trying, and don't give up because of a momentary setback. For example, you can say, "I believe that as long as you continue to Xi work hard to learn and improve yourself, you will definitely be able to achieve better grades and performance." I have always been there for you to support you, and I believe that you will be able to achieve your dreams. Such an answer can make your girlfriend feel supported and encouraged, and it can also give her more motivation and confidence to pursue her goals.