The 1960s Were a Turning Point in Nuclear Arms Talks

The 1960s were a turning point in nuclear arms talks for what reason?

A) The resources being poured into the Vietnam War made it necessary for both the United States and the Soviet Union to reduce their nuclear stockpiles,so no talks were necessary.
B) Reconnaissance satellites made it possible for nations to monitor the weapons possessed by other nations,which made cheating on agreements more difficult.
C) The SALT talks between Henry Kissinger and the Soviet Union fell through when Kissinger was unable to reach any kind of agreement with the Soviets.
D) Both the United States and the Soviets had sufficient weaponry to ensure second-strike capability,which meant deterrence was successful and talks were unnecessary.