Which of the Following Is Most Likely to React as a Nucleophile

Multiple Choice

Which of the following is most likely to react as a nucleophile rather than a base? $$\begin{array} { c c c c } \mathrm { KOC } \left( \mathrm { CH } _ { 3 } \right) _ { 3 } & \mathrm { CH } _ { 3 } \mathrm { COO } ^ { - } & \mathrm { DBU } & \mathrm { DBN } \\\text { I } & \text { II } & \text { III } & \text { IV }\end{array}$$

A) I
B) II
C) III
D) IV