Roj yeeb nkab Ib txoj hlua ntev ntawm cov hlau uas muaj qhov khoob thiab tsis muaj pob qij txha nyob ib puag ncig.Nws yog dav siv nyob rau hauv kev tsim khoom ntawm cov khoom siv thiab cov khoom siv kho tshuab, xws li cov kav dej tho roj, tsheb tsav shafts, tsheb kauj vab ncej, thiab steel scaffolding ...
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