Cov khob khob, tseem raug hu hais kua mis. Cov ntaub ntawv yog ua los ntawm ntau cov ntaub ntawv, suav nrog cov khoom siv yas uas muaj ntau yam zoo li cov ntaub ntawv so kom zoo li cov nroj tsuag (py) 1}}. Cov ntaub ntawv xaiv nyob ntawm ntau yam, xws li ntsuas kub ntawm cov zaub mov, txawm hais tias rov ua dua tshiab lossis biodegradebion yog yuav tsum tau, thiab lwm yam.
