Chinese ranking traditionally uses the Heavenly Stems (天干): 甲 to 乙 to 丙 to 丁, where 甲 is the top. So 甲级 = A-grade, 乙级 = B-grade, 丙级 = C-grade. Real estate, sports leagues, and professional certifications all use this system.
memory
甲 originally drew a seed husk cracking open - first growth, hence 'first / top'. Same character used for 'armor' and the first Heavenly Stem.
