The basic course of mathematics and physics in Tsinghua is mainly competition enrollment, that is, it mainly recruits students who walk in. They study the basic courses of mathematics and physics in freshmen and sophomores. The basic course is actually the combination of physics college and mathematics college. Tsinghua will turn all science majors into basic courses in the next step, and the total number may reach ten. Although basic courses are optional, at present, most of the students who apply for basic courses are competition students with a solid foundation in mathematics, physics and chemistry. They are also interested in future theoretical research in mathematics or physics. Therefore, students who don't want to develop in this field should find a major first, because if you really change majors after two years, you will miss many professional courses and others will fall behind. In fact, Tsinghua is still very open in changing majors. If the major you choose doesn't suit your preference, you will have a chance to change careers. As for key disciplines, Tsinghua has turned all sciences into basic courses in order to revitalize science in Tsinghua, so we should attach great importance to it. But it doesn't matter. The key depends on whether you want to develop in this field.