How did leonid brezhnev demonstrate his use of the brezhnev doctrine? by signing the salt treaties by abandoning the space race by curbing military spending by sending soviet troops to afghanistan

The correct option is Dsoviet invasion of Afghanistan in 1979

The principles of the doctrine, which mainly justified soviet intervention in maintaining a socialist country, especially the eastern block, were so broad that the Soviets even used it to justify their military intervention in the non-Warsaw Pact nation of Afghanistan in 1979.