The difficulty level is high. The second order of 660 is the learning content in high number, and the second order of 660 is the problem of curve and surface integral part of the series of number one, and the difficulty levels of various curves involved are higher. Doing this kind of problems requires students to have a solid foundation and good abstract thinking. The second order of 660 refers to the high number test questions, which mainly includes the integration and the application of various functions. The difficulty of the topic is moderate, and some of them are difficult.