複選題19. Environmental scientists monitor water pollutants using UV-Vis and IR spectroscopy. Which of the following reflect appropriate uses of these techniques? (A) IR can quantify nitrate contamination in water by its characteristic absorbance. (B) IR spectra help identify functional groups like -OH, -C=O, or -C=C- in water pollutants. (C) Adding acid to the water leads to a blue shift in UV spectra of a pollutant, suggesting it's becoming less reactive or less conjugated. (D) Absorption increase in the UV spectra may indicate a breakdown of the dye structure. (E) IR can monitor the dye concentration over time using Beer's Law.