https://www.vshkole.org/11-klass/himiya-11klass/yuv-isayenko-st-goga-2010-test-kontrol/variant-2-yuv-isayenko-st-goga-2010-test-kontrol/kontrolni-roboti-variant-2-yuv-isayenko-st-goga-2010-test-kontrol/kr1-55/