1, Chongde Jingyou Volume: The main reason for the difficulty is that it has a wide scope of investigation, covering all the knowledge points of high school mathematics, and the test questions are difficult, requiring candidates to have a solid mathematical foundation and high thinking ability. The writing style of Chongde jingyou's thesis is also very unique, which requires candidates to have the ability to flexibly use mathematical knowledge to solve problems.

2. Qiantang Yongzhen: As a high school mathematics competition guidance book, its topic is difficult, requiring candidates to have a solid mathematical foundation and high thinking ability.