Anger's sketch is especially recommended abroad (the purpose of sketch practice is different, but Anger's sketch proportion and body pursuit and performance are very strict)
These two domestic painters pay more attention to the ability of line modeling, while Angel is better at using the expression of structure, volume and modeling pursued by the West. The application of proportion and line is affirmative and rigorous.
These works have a lot to learn from. If you want to learn sketch, you'd better not buy some so-called "teaching materials" casually. Some students are not as good as those in the Academy of Fine Arts.
Since we are studying, we should always keep a serious attitude and a rigorous spirit. Needless to say, the achievements of the three painters I recommend in painting are all solid, which deserves our in-depth study and research.