obligation

n.义务，职责；恩惠

obey, obfuscate, obfuscation, obiter dictum, obituary, object, object glass, object lens, object lesson, object to, object to sth., objection, objectionable, objectionably, objective, objectively, objectivity, objector, objet d'art, oblate, obligate, obligatory, oblige, obliged, obliging, obligingly, oblique, oblique angle, obliquely, obliqueness, obliquity, obliterate, obliteration, oblivion, oblivious, obliviousness, oblong, obloquy, obnoxious, obnoxiously, obnoxiousness,