How did the nuclear arms race cause tension

John Swift examines a vital element of the Cold War and assesses the motives of the Superpowers. Nuclear weapon test, 1956The destruction of the Japanese cities of Hiroshima and Nagasaki by American atomic weapons in August 1945 began anarms race between the United States and the Soviet Union.

Ihave no idea what the answer is

Why you put last one a? i think is b.