1. Crystal iav Crystal khob kuj yog ib khob.Cov khoom xyaw tseem ceeb yog silicon dioxide, tab sis qhia txog cov hmoov lead, cymbal, zinc, titanium thiab lwm yam khoom siv.Vim tias cov iav no muaj qhov pom tseeb thiab qhov pom tseeb, nws qhov kev pom sab nraud yog huv si thiab siv lead ua, yog li nws yog ...
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