Disarmament refers to the process of reducing or eliminating weapons, especially nuclear weapons. It is an important aspect of international peace and security. The options given in the question are all related to disarmament except for one. Let's understand each of them in detail:

a) SALT (Strategic Arms Limitation Talks): These were a series of negotiations between the United States and the Soviet Union during the Cold War to limit the number of nuclear weapons in their arsenals. The talks led to the signing of two treaties- SALT I and SALT II.

b) NPT (Non-Proliferation Treaty): This is an international treaty aimed at preventing the spread of nuclear weapons and promoting disarmament. It has been signed by 191 countries, including the five nuclear-weapon states- US, Russia, China, France, and the UK.

c) CTBT (Comprehensive Nuclear-Test-Ban Treaty): This is a treaty that bans all nuclear explosions, whether for military or civilian purposes. It has been signed by 184 countries and ratified by 168. However, it has not yet entered into force as eight countries, including the US and North Korea, have not ratified it.

d) NATO (North Atlantic Treaty Organization): This is a political and military alliance of North American and European countries. It was formed in 1949 to counter the Soviet Union during the Cold War. While NATO has played a role in arms control and disarmament, it is not primarily focused on this issue.

Therefore, the correct answer is option 'd' - NATO is not related to disarmament.