Without having a timeframe or choices, I would guess it would be the Holocaust which was from 1941-1945 when the German Nazi's rounded up and excecuted Jews (men, women, and children)
Arbitration generally occurs between a union and management when "<span>a. the two sides have failed to settle their dispute and produce a new contract," since this means that the two sides submit their grievances to a third party, the mediates the conflict. </span>
I believe D OR C but I think it’s C