These ranks range from A-D (D being the lowest rank possible to still pass the level), with an additional 'S' rank for extremely good performance.
ðiːz ɹˈæŋks ɹˈeɪndʒ fɹʌm ˈeɪdˈiː dˈiː bˌiːɪŋ ðə lˈoʊɪst ɹˈæŋk pˈɑːsᵻbəl tə stˈɪl pˈæs ðə lˈɛvəl, wɪð ɐn ɐdˈɪʃənəl ˈɛs ɹˈæŋk fɔːɹ ɛkstɹˈiːmli ɡˈʊd pɚfˈoːɹməns.