Why Were the Russians Not Concerned About the Threat of Nuclear

Why were the Russians not concerned about the threat of nuclear war with the United States?

A) They understood the destruction that it would cause and knew the United States would never do it.
B) They did not understand how much destruction it would cause.
C) They had spies providing them information to build their own nuclear weapons.
D) They knew the American public would never approve of such an action.
E) They were not concerned with the amount of lives lost in such a war.