threeleaf三叶threenum.三n.三；三个adj.三个的three billion dollars3亿美元Three layer framework三层结构three-day treatment[医] 三日疗法(治烧伤)three gorges dam area三峡库区three transformations三个转变Three GorgesReservoir三峡库区three-in-one unit三用装置three semester system三学期制three - arch tunnel三联拱three-lobe oil pump三叶齿轮油泵