The oxidation number is changed in which of the following case

(A) SO2 gas is passed into $C{r}_{2}{O}_{7}^{2-}/{H}^{+}$

(B) Aqueous solution of $Cr{O}_{4}^{2-}$ is acidified

(C) $Cr{O}_{2}C{l}_{2}$ is dissolved in NaOH

(D)$C{r}_{2}{O}_{7}^{2-}$ solution is made alkaline