Question

which treaty was passed in 2010, further reducing the number of nuclear weapons a country could have?
new start
new salt
new limited test ban

Explanation:

The New Strategic Arms Reduction Treaty (New START) was signed in 2010. It aimed to further reduce the number of nuclear weapons. New SALT (Strategic Arms Limitation Talks) was an earlier initiative. The Limited Test Ban Treaty was from 1963.

Answer:

New START