C. The mediator is the answer because even though the question is trying to gauge whether you know the meaning of the word mediator, it is also providing a grammatical solution to itself. None of the other words fit in that sentence correctly except for mediator, and also the word mediator (someone who is keeping peace between differing parties) fits the actions the sentence is proposing.
I can infer that they may be scared or surprised because the pictures they looked taken aback and surprised. They probably got scared but are having fun because they payed to do this.
