Which statement is correct for the following reaction?

$${\text{2ClO}}_3^ - {\text{(aq)}} + {\text{S}}{{\text{O}}_{\text{2}}}{\text{(aq)}} + {{\text{H}}^ + }{\text{(aq)}} \to {\text{2Cl}}{{\text{O}}_{\text{2}}}{\text{(g)}} + {\text{HSO}}_4^ - {\text{(aq)}}$$

A.     ${\text{ClO}}_3^ -$ is the oxidizing agent and it undergoes reduction.

B.     ${\text{ClO}}_3^ -$ is the reducing agent and it undergoes oxidation.

C.     ${\text{S}}{{\text{O}}_{\text{2}}}$ is the oxidizing agent and it undergoes oxidation.

D.     ${\text{S}}{{\text{O}}_{\text{2}}}$ is the reducing agent and it undergoes reduction.

A