When the Japanese empire was dismantled at the end of World War Two, Korea fell victim to the Cold War. It was divided into two spheres of influence along the 38th parallel. The Americans controlled south of the line - the Russians installed a communist regime in the north, later ceding influence to China.
Your answer would be B.
Why? The others don't make sense.
The correct answer is - D. It was widely agreed that a traditional invasion of Japan would drag the war on for years and lead to may, may more deaths than the atomic bomb.
The US officials decided to use the atomic bombs on Hiroshima and Nagasaki in Japan because of two reasons. The first and more important one was to put an end to the war as quickly and efficiently as possible, minimizing the deaths of their troops as much as possible. The second one was to create an image of a country that reached a level of global military power, in order to boost its global reputation and cause fear at other nations.
Both of those things worked out very fine for the USA. They ended the war with Japan in no time, and they gained a status of a global military powerhouse.
Roosevelt's personality and political philosophy fitted the imperatives far more than they did the fashions of the times, so that the degree to which his behavior in the White House both hastened and shaped the dramatic growth of presidential power over the next seventy-five years must be seriously considered. Temperamentally, Roosevelt craved attention. Once in the White House, especially in view of the changed national and international circumstances, he could not fail to focus national attention on the presidency.
Answer:
Option D is the right answer