fifthnum.第五n.五分之一fifth threat of radar雷达的第五大威胁fifth nerve paralysis第V对脑神经麻痹fifth metacarpal bone第五掌骨fifth-order sequence五级层序fifth-year art major五年制艺术专业fifth wheel instrument五轮仪Fifth left aortic arch第五左主动脉弓fifth wheel of a coach多余的东西fifth venereal disease第五性病Fifth costal cartilage第五肋软骨