Txoj kev npaj thoob ntiaj teb

Tom qab ntau tshaj 20 xyoo ntawm kev txhim kho kev lag luam thiab kev siv tshuab, Dahe lub tuam txhab tau tsim ntau tshaj 100 hom khoom siv ntsia hlau, uas muag tau zoo hauv Suav teb, thiab xa tawm mus rau Is Nrias teb, Russia, Tebchaws Meskas, Canada, Australia, Is Nrias teb, Kazakhstan, Africa thiab lwm yam ntau tshaj 20 lub tebchaws thiab thaj chaw, tau txais kev qhuas los ntawm cov neeg siv khoom hauv tsev thiab txawv teb chaws.