A. Developing a vaccine to prevent Polio. I just took the test :)
D. His mission to discover the truth of what happened (I'm 100% sure)
Answer: A) The Cuban Missile Crisis
Context/detail:
The Cuban Missile Crisis was a tense face-off between America, led by President John F. Kennedy and the Soviet Union, led by Nikita Khrushchev, in October of 1962, over the placement of Soviet missiles on the island of Cuba, close to the United States home territory. It is often stated that this moment was the closest the USA and the USSR ever came to the eruption of an actual nuclear war between the two superpowers.
The correct option is D
In 1931, Japan suffered the decline of exports due to the decline of trade in the Great Depression and the protectionist measures that the powers put in place to try to alleviate it. The commanders of the Kwantung Army, which protected the South Manchurian Railway, decided to occupy it, in the hope that the region would serve as a source of food and raw materials and as a market for Japanese products. The military command believed that the invasion would allow to reach the autarky that he considered necessary for the future war with the Western powers that he was convinced would explode.