Why Were the Soviets Unconcerned About the Threat of Nuclear

Why were the Soviets unconcerned about the threat of nuclear war with the United States?

A) They had regained the favor of the United States by allowing non-Communists to participate in the political process.
B) They did not understand how much destruction nuclear war would cause.
C) They were spying on U.S.scientific progress and developing their own nuclear weapons.
D) They knew the American public would never approve of such an action as nuclear war in the future.
E) They were not concerned about the amount of lives lost in nuclear war.