I suggest you grasp the foundation, because your grades are not very stable. You can try the textbook. I think it's very effective. Actually, I don't have to think too much. I didn't do well in the exam at all. Originally, I was very open-minded because I believed in my own strength, but this exam was a bit abnormal and my state was not very good.

The exam is unstable, either your state is not very good, or the difficulty of the exam is different, so you'd better see what it is. If it is the former, find some videos and adjust them well; If it is the latter, you should learn to give up and get something, because you can't, and in fact many people can't. You just have to do what everyone knows is right. From experience.