Answer: (1) Necessity: China students' practical ability and comprehensive application ability are relatively weak. Therefore, when planning the new curriculum system, the Outline of Basic Education Curriculum Reform (Trial) stipulates that "comprehensive practical activities should be set up as a compulsory course from primary school to high school", emphasizing students' practice, enhancing students' awareness of inquiry and innovation, learning scientific research methods and developing their comprehensive application ability. Strengthen the close relationship between school and society, and cultivate students' sense of social responsibility.

At the same time, the Outline of Basic Education Curriculum Reform (Trial) also points out that comprehensive practical activities and various disciplines should form an organic whole, which is relatively independent and closely related. In some cases, comprehensive practical activities can also be carried out in combination with the teaching of certain disciplines, and at the same time, students' practical and comprehensive application ability should be cultivated in various disciplines. Therefore, the curriculum standard has adjusted the subject structure of mathematics, and set up the mathematics learning field of "synthesis and practice" in addition to the knowledge fields of "number and algebra", "figure and geometry" and "statistics and probability".

Teaching features:

(1) comprehensiveness: The exploration of any subject must reflect the internal unity of individuals, society and nature, and the internal unity of science, art and morality.

(2) Practicality: The development of comprehensive practical activity curriculum often takes various activities as the carrier, emphasizing that students learn through activities or personal experience, not for "activities" and "activities".

(3) Openness: The comprehensive practical activity course faces the whole life world of students, and its content is closely related to students' personal life or real society, which is often manifested as an open question with no fixed answer. To solve such an open problem, students can't go to books to find ready-made answers, only through their own efforts can they find possible answers.

(4) Generative: The development of comprehensive practical activity curriculum rarely starts from the predetermined curriculum objectives, and often revolves around an open theme or problem. With the continuous development of activities, new goals, new problems and new themes are constantly produced, students' understanding and experience are constantly deepened, and creative sparks are constantly generated, which is a concentrated expression of the "generative" nature of the comprehensive practical activity curriculum.

(5) Autonomy: The implementation of comprehensive practical activity curriculum attaches great importance to students' existing interests and experiences, and emphasizes students' independent choice and exploration. Students can not only choose the content, progress and way of learning, but also evaluate and reflect on their own learning process or results.