知识贝壳
知识贝壳
所属栏目：建筑施工英语
Thestrongestathletescanliftcloseto455kgjustofftheground,butfewordinarypeoplecanliftmorethanabout68kg.Earlymansoondevelopedmachinesforliftinglargestonesandtreetrunks.Asimpledeviceisasinglepulleywheelarrangedasahoist.Butaropearoundonepulleymerelychangesthed ......（本文共 5981 字 ） [阅读本文] >>