Tus nuv txhaj koob tshuaj tivthaiv cav tshuab yog kev teeb tsa nrog kev ua haujlwm yooj yim.
Nws yog qhov tsim nyog rau ntau yam haujlwm kev ua haujlwm. Xws li: cov nruas pov tseg, kev zam txim, kev sib dhos, khoom siv kho cua sov, suav nrog cov khoom ua kom yooj yim thiab tsis xwm yeem, cov qauv hlau.