Sodium Thiosulfate, Na₂S₂O₃, Is Used as a "Fixer" in Black

Sodium thiosulfate, Na₂S₂O₃, is used as a "fixer" in black and white photography. Identify the reducing agent in the reaction of thiosulfate with iodine. 2S₂O₃^2-(aq) + I₂(aq) → S₄O₆^2-(aq) + 2I^-(aq)

A) I₂(aq)
B) I^-(aq)
C) S₂O₃^2-(aq)
D) S₄O₆^2-(aq)
E) S₂O₃^2-(aq) and I^-(aq)