Какие оценки в Америке

In USA teachers use letters as marks. These marks, which are called grades, are O, S, A, B, C, D, E, F and U. U stands for Unfair and it means that a pupil didn't give even one correct answer. F equals to Fail and it is like mark 2 in Russia. E is Enough, D - Diverse, C - Creditable and these marks stand for 3. B (brilliant) and A (artful) stand for 4. The best marks are S (supreme) and O - the best of the best, when all the answers are correct.