I. Kev npaj ua ntej pib 1, txheeb xyuas cov kev qhia tshwj xeeb, tuab, thiab cov khoom siv ntawm cov kav hlau uas tsim los ntawm lub tshuab ua haujlwm; Txiav txim siab seb nws puas yog cov yeeb nkab kev cai, seb nws puas yuav tsum tau teeb tsa cov hlau stamping pwm, thiab seb puas muaj lwm yam tshwj xeeb technica ...
Nyeem ntxiv