Daim duab saum toj no qhia txog cov khoom siv sib txawv nrog qhov sib txawv hardness, Kub kam rau ua, xim xim, kom zoo dua, nqe theem thiab txee lub neej. Thaum koj tsis paub meej tias yam khoom twg yuav tsum tau siv rau koj cov khoom, cia li saib daim duab no.
