Proteins Containing a Certain Functional Group (Identified as RSH) Can $\rightarrow$

Proteins containing a certain functional group (identified as RSH) can be titrated with a triiodide ion to produce another functional group (identified as RSSR) .The reaction equation is given below.What is oxidized and what is reduced in this reaction? 2 RSH(aq) +I₃^-(aq) $\rightarrow$ 3I^-(aq) + RSSR(aq) +2H⁺(aq)

A) RSH is oxidized; I₃^- is reduced.
B) RSH is reduced; I is oxidized.
C) Both RSH and I are oxidized.
D) Both RSH and I are reduced.
E) This reaction is not oxidation-reduction.