Can the DM add any <C> dice to this action? If so how/why?

I understand he can add [M] for various factors, such as the pc is on ice or mud or a moving coach, but I can't see how <C> would be added.

Thanks for any advice/ direction on this.

Generally, <P> challenge dice are not added, only misfortune, unless its an opposed test or the action calls for it. I'm not sure in what situation I would add a <P> to a Guarded position action. I suppose you could make it an opposed check vs opponent's weapon skill