Cais tawm cov kab txuas nrog cov dej xau thiab txwv tsis pub nkag mus rau nws.
Nws raug nquahu tias cov neeg teb thawj zaug hnav zoo rau kev ua pa rau tus kheej ua pa tawm apparatus thiab tiv thaiv khaub ncaws. Zam kev ua hmoov av; cheb kom huv si thiab lub hnab ua ntej tsiv mus rau qhov chaw nyab xeeb. Yog tias muaj ib qho xau loj loj, npog nws nrog qhwv yas lossis canvas. Sau rau kev rov siv dua lossis thauj mus rau qhov chaw rov ua dua tshiab rau kev pov tseg.