相关单词同义词selectable, hit, or, miss, elective subjects, 近义词 voluntary 自愿的, elective 选举的, discretionary 自由裁量的, possible 可能的, free 自由的反义词obligatory, 强制性的compulsory, 强制的临近词opulence, option, optionally, optionality, optional fee, optional rate, optional halt, optional part, optional list, optional bond, optional tour, optional meet相似词optimization, optimize, optimum, option, optometrist, opulent, opus, or, 返回 optional