To put it simply: freshman is a public basic course, such as advanced mathematics and English, but there is also a mechanical drawing, which should be regarded as a mechanical basic course.

Sophomore is mainly specialized basic courses, such as physics (a lot of physics, it seems that both freshmen and sophomores have it), electrician/electronics, mechanical principles, engineering mechanics, material mechanics and so on.

Junior and senior are professional elective courses and some courses that need to learn professional basic courses first, such as fluid mechanics and so on.

The specific class is too long, I forgot, anyway, it is probably such a train of thought.