Identify the Missing Reagent in the Reaction Shown Below $\mathrm{HCO}_{2} \mathrm{Et}$

Multiple Choice

Identify the missing reagent in the reaction shown below.

A) ethyl formate, $\mathrm{HCO}_{2} \mathrm{Et}$
B) diethyl carbonate, $(\mathrm{EtO}) _{2} \mathrm{C}=\mathrm{O}$
C) diethyl oxalate, $\mathrm{EtO}_{2} \mathrm{CCO}_{2} \mathrm{Et}$
D) ethyl acetate, $\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{Et}$