I like candy too.
#1 - C is the correct answer because it fills a little gap/strengthens the reasoning of the conclusion. The conclusion is that beginning the mediation late in the process would be "ineffective." So, as C states, beginning late is a bad thing because your opponents position "hardens" during this lag in time.
Choice A - This is very general, and has nothing to do with the timeframe of the mediation process described in the conclusion.
Choice B - Same as A, very general, and it doesnt directly help strengthen/justify the conclusion.