There may be a difference in grading methods between European and USA colleges & universities. In the UK when I took classes way back in history, and more recently my daughter, credit was awarded solely on exam results. Whereas in the USA grading is usually a mix of homework, class participation, and exams including open book exams. The USA method makes it easier to obtain higher grades. One USA class I took you were exempt from exams if you maintained high marks in homework (probably the hardest class I ever took).