which of the following is the Reagent of the reaction?

${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}+{\mathrm{CH}}_3\mathrm{COOH}\stackrel{?}{\to }{\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5+{\mathrm{H}}_2\mathrm{O}$

Alcohol and carboxylic acid combine to form an ester with a fruity smell. Esterification is the process of turning this substance into an ester. 

In the presence of concentrated ${\mathrm{H}}_2{\mathrm{SO}}_4$, ethanol and ethanoic acid combine to generate the ester ethyl ethanoate.

$\begin{array}{rcl} & & {\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}+{\mathrm{CH}}_3\mathrm{COOH}\stackrel{\mathrm{Conc}. {\mathrm{H}}_2{\mathrm{SO}}_4}{\to }\\ & & {\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5+{\mathrm{H}}_2\mathrm{O}\end{array}$