Answer : The correct option is, carbon (C)
Explanation :
Oxidizing agent : Oxidizing agent are the agent that gains electrons and is reduced in a chemical reaction.
Reducing agent : Reducing agent are the agent that lose electrons and is oxidized in a chemical reaction.
The given balanced chemical reaction is,

First we have to calculate the oxidation number of sulfur and carbon.
The oxidation state of 'S' in
and
are, (+6) and (-2) respectively.
The oxidation state of 'C' in
and
are, (0) and (+2) respectively.
From this we conclude that, the
act as an oxidizing agent and 'C' act as a reducing agent.
Hence, the reducing agent in the following reaction is, carbon (C)