Cov khoom siv hluav taws xob vuam tshuab yog yooj yim siv, txhim khu kev qha, dav siv hauv kev tsim khoom thiab kev ua haujlwm, xws li kev tsim kho, kev lag luam nkoj, yog hom kev ua haujlwm tseem ceeb heev. Txawm li cas los xij, welding ...
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