Uhlobo lwevalvu yesityalo sekhemikhali kunye nendawo yokusetyenziswa (kunye nohlobo olusebenzayo)
Uhlobo lwevalvu yezityalo zemichiza kunye nendawo yokufakwa (ngohlobo olusebenzayo) Emva kokuveliswa kweenjini zomphunga, kwiminyaka engamashumi amabini okanye engamashumi amathathu edlulileyo, ngenxa yemfuneko ye-oyile ekrwada, izityalo zekhemikhali, amaziko ombane, ishishini lesinyithi, iinqanawa, amandla enyukliya ge. ..
jonga iinkcukacha