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.
Answer: Reagan did not stop communism (communism never existed and its ideology is still here....there are many communist parties all over the world which is quite surprising and incredible) but practiced very well Kennan´s strategy of "containment". Communism itself underwent serious crises (1956 Hungary, 1968 Czechoslovakia, 80s in Poland) ...in 1980s there was a lot of dissatisfaction in the Eastern block, anti-communist opposition was growing and USSR became aware that reforms are necessary. Gorbatchev (from 1985) was really aware that the communist regimes are no longer sustainable. There were various factors.
Explanation: communist regimes exhausted themselves, nothing worked....economically and ideologically as well. That was something which helped very much to Reagan.
Russian leaders adopted the idea of strong, centralized control of the empire.