Answer:
D. Fear of a nuclear war between the two nations
Step-by-step explanation:
The evident power that these arms granted began an enormous arms race between the powers that were already guessed at in the Cold War, both with respect to the atomic weapons themselves and to the launch vectors that allow them to be carried to their targets and extensive technical and human resources, necessary to operate them effectively. The Soviet Union, which had been closely following the Manhattan Project since at least 1943 and had already developed its own investigations at the Kurchátov Institute, managed to detonate a replica of the Nagasaki bomb ("Joe 1") on the Semipalatinsk polygon, in the morning of August 29, 1949. However, the USSR developed in parallel a completely own design weapon ("Joe 2") that detonated on September 24, 1951, releasing 38 Kt. The Nuclear Cold War had begun. They were followed by the United Kingdom on October 3, 1952 ("Operation Hurricane"), France on February 13, 1960 ("Gerboise Bleue") and China, on October 16, 1964 ("Device 596").
This took for granted that both blocks were prepared to face a total nuclear war, which produced a great level of fear, because of the destructive capacity possessed by this type of weapons.