Correct Option: C
$L (D) = L (G).$ Both must represent same language. Also, if we are converting a grammar from ambiguous to unambiguous form, we must ensure that our new new grammar represents the same language as previous grammar.
For ex $G1: S \rightarrow Sa\mid aS\mid a;$ $\{$Ambiguous $(2$ parse trees for string '$aa$'$)\}$
$G1': S \rightarrow aS\mid a;$ $\{$Unambiguous$\}$
Both represent the language represented by the regular expression: $a^+$