For the first one I think it's guards. Verbal de-escalation skills are usually used to solve a problem with a patient, who I think is mental or ill or agitated. This could be prisoners as well, so guards probably have to be trained in these skills.
For the second one, I think the answer is " it was easier to detect conflict and intervene." To me, I don't know why they put that option in there it's probably wrong.
