Tam sim no qhov zoo ntawm cov xim phab ntsa tau nce siab dua, tab sis nws tseem tsis tuaj yeem ua tau raws li qhov xav tau zoo ntawm cov tswv, tshwj xeeb tshaj yog qhov flatness thiab smoothness ntawm phab ntsa, tab sis qhov no tsis yog tsuas yog cuam tshuam rau qhov zoo ntawm cov xim ntxiv, vim tias. lub...
Nyeem ntxiv