The correct answer is option 4: NATO. NATO, which stands for North Atlantic Treaty Organization, has not been disbanded. NATO is a military alliance between North American and European countries, founded in 1949. Its purpose is to promote peace and security among its member states through collective defense. NATO members are committed to defending each other in case of an armed attack and work together to address global security challenges.

CENTO, option 1, stands for Central Treaty Organization and was disbanded in 1979. It was a military alliance between Iran, Iraq, Pakistan, Turkey, and the United Kingdom to promote stability and security in the Middle East.

The Warsaw Pact, option 2, was an alliance of communist states in Central and Eastern Europe, led by the Soviet Union. It was disbanded in 1991 following the collapse of the Soviet Union.

SEATO, option 3, stands for Southeast Asia Treaty Organization. It was disbanded in 1977 and was an alliance of countries in Southeast Asia and the United States to prevent the spread of communism in the region.

Therefore, the only military alliance that has not been disbanded among the options provided is NATO (option 4).