Answer:
The correct answer is the last option: Involving a third party.
Step-by-step explanation:
To begin with, the major difference between the terms of negotiation and mediation is that in the last one there is a third party involved that seeks for the most quickly and benefitial deal for the both parties that are discussing, while in the negotiation there is not a third party and the two parties existing seeks for their own benefits, even if that means to harm the other person in the process of getting the best for one of them. That is why that the mediation needs to use a third party that has to be impartial to the situation and only wants the best for the parties in the conflict.