Which is the oxidizing agent in the following reaction?

$${\text{5S}}{{\text{O}}_2}{\text{(g)}} + {\text{2IO}}_3^ - {\text{(aq)}} + {\text{4}}{{\text{H}}_2}{\text{O(l)}} \to {\text{5SO}}_4^{2 - }{\text{(aq)}} + {{\text{I}}_2}{\text{(aq)}} + {\text{8}}{{\text{H}}^ + }{\text{(aq)}}$$

A.     ${\text{S}}{{\text{O}}_{\text{2}}}$

B.     ${\text{IO}}_{\text{3}}^ -$

C.     ${{\text{H}}_{\text{2}}}{\text{O}}$

D.     ${\text{SO}}_{\text{4}}^{2 - }$

B