Ans: D
$\begin{array}{cl}
& 0.002\ 345\ 678\ 9 \\
= & 0.002\ 346 \ \text{(correct to 6 decimal places)} \\
& 0.002\ 345\ 678\ 9 \\
= & 0.002\ 345\ 68 \ \text{(correct to 6 significant figures)}
\end{array}$
$\begin{array}{cl}
& 0.002\ 345\ 678\ 9 \\
= & 0.002\ 346 \ \text{(correct to 6 decimal places)} \\
& 0.002\ 345\ 678\ 9 \\
= & 0.002\ 345\ 68 \ \text{(correct to 6 significant figures)}
\end{array}$
