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

Proteins containing a certain functional group (identified as RSH) can be titrated with 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?
2RSH + I₃^- $\rightarrow$ 3I^- + RSSR + 2H⁺

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.