Consider the following nucleophiles:
$$
\begin{array}{cccc}
\mathrm{H}_2 \mathrm{O}, & \mathrm{CH}_3 \mathrm{COO}^{-}, & \overline{\mathrm{OH}}, & \mathrm{CH}_3 \mathrm{O}^{-} \\
\text {I } & \text { II } & \text { III } & \text { IV }
\end{array}
$$
The correct order of decreasing nucleophilicity is,
(a) I $>$ II $>$ III $>$ IV
(b) IV $>$ III $>$ II $>$ I
(c) IV $>$ I $>$ II $>$ III
(d) IV $>$ II $>$ III $>$ I