If there is no way to solve the problem, there are usually two reasons:
The first kind is a single knowledge, but it will not be used together, which means that you usually practice less and your knowledge is not deep enough, and you haven't reached the point of giving inferences;
Second, because you have read fewer questions, it is the first time to read them. The process of solving problems consumes too much thinking time, and it is easy to get bored or don't want to continue thinking deeply. The solution is to do more different types of exercises, not to make up for it by a single repeated question type, but to expand your thinking through a variety of flexible questions, and at the same time limit yourself a time to solve problems. Only by constantly completing the answers to different questions within the specified time can your efficiency be improved.
If it is because of your carelessness that the process goes wrong and ultimately affects the result, then you need to be more careful when solving the problem. Of course, I think this reason is unlikely. After all, you can fill in the blanks!