whiCh oF thE Following is truE ABout ACiD rAin A.it is ACknowlEDgED By sCiEntists to BE thE most sErious pollution proBlEm thAt humAn BEings now FACE. B.mAny EnDAngErED spECiEs ArE on thE vErgE oF ExtinCtion BECAusE oF ACiD rAin. C.ACiD rAin is ComposED oF sulFur DioxiDE AnD nitrogEn oxiDEs mixED with wAtEr vApor FounD in thE uppEr AtmosphErE. D.ACiD rAin is mostly FounD in thE unitED stAtEs AnD CAnADA.