1 and 660 are sets of multiple-choice questions and fill-in-the-blank questions. The questions in 660 pay more attention to the foundation, covering all the knowledge points covered by the postgraduate mathematics, which will be more difficult and suitable for the learning objectives at this stage.
2880 is a multiple-choice fill-in-the-blank question. The questions in 880 are divided into basic questions, comprehensive questions and extended questions, which are suitable for strengthening stage exercises and training your problem-solving ability.