The correct alternatives are A) The United Nations sent troops to help South Korea and D) Peace Negotiations were attempted but it took two years for an armistice to be signed.
In June 25, 1950, North Korea invaded the south and overran most of the country. In September 1950 the United States led a United Nations force to intervene which had a composition of around 90% American troops. The war was viewed the war as a communist aggression and thus considered illegitimate, justifying its action, since the Soviet Union had boycotted the UN.
There were armistice negotiations attempts for two years, firstly in Kaesong and then in Panmunjom. A major, negotiation point was the repatriation of the war prisoners, which the terms could not be agreed upon due to the high number of PVA ([Chinese] People's Volunteer Army) and KPA ([North] Korean People's Army) soldiers who refused to go back to the north, which was unacceptable to the Chinese and North Koreans. Finally on the 27th of July, 1953, a Neutral Nations Repatriation Commission was set up and the armistice was settled upon.
