The first difference is that the overall level of English is different. Class A has the best English, Class B the worst and Class C the worst.
The second difference is that the time for taking CET-4 is different. Freshmen in Class A take the final exam of the second semester, sophomores in Class B take the final exam of the first semester, and sophomores in Class C take the final exam of the second semester.
The third difference is that the learning progress is different. A class has a section where foreign teachers come to class.
Extended data:
The purpose of college English ABC class is to select students with higher scores to take CET-4 in advance. Students with low scores will study for a year or two before taking the exam, so that students with high scores will not be delayed, and students with low scores will be given a buffer time, so that the school can admit a higher proportion of students of Band 4 and Band 6.
The entrance English exam must be prepared in advance. If students from other places can do the questions in previous years first, because there may be some differences in the ways of English exams in different places, they should adapt in advance, otherwise they will suffer a lot.