6. The Nobel Prize in chemistry 2010 was awarded to "Palladium-catalyzed cross-coupling reactions in organic synthesis". Please give the oxidation state of palladium in each of the following transition-metal catalysts. (A)PdCl2  (B)Pd(OCOCH3)2 (C) Pd(OCOCF3)2 (D) Pd(PPh3)4